Quarterly report pursuant to Section 13 or 15(d)

Stock-based Compensation - Additional Information (Details)

v3.19.2
Stock-based Compensation - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
Dec. 31, 2017
Jun. 30, 2019
Mar. 31, 2018
Jun. 30, 2019
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock-based compensation expense       $ 2,739,000 $ 2,186,000
Number of shares, Unvested   0   0  
Stock Options [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Minimum age required for employees to qualify for immediate vesting of RSUs       55 years  
Threshold years required for retirement age       70 years  
Options exercised, aggregate intrinsic value       $ 200,000 $ 900,000
Weighted-average grant-date fair value       $ 11.37 $ 18.78
Unrecognized compensation expense related to stock options   $ 6,800,000   $ 6,800,000  
Weighted average period of unrecognized compensation expense expected to be recognized       1 year 10 months 24 days  
Options granted       390,814  
Performance Shares [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Unrecognized compensation expense related to stock options   $ 100,000   $ 100,000  
Number of options outstanding, non-vested options   41,250   41,250  
Stock-based compensation expense   $ 56,000   $ 100,000  
Grant date fair value   $ 200,000   $ 200,000  
Restricted Stock Units (RSUs) [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Minimum age required for employees to qualify for immediate vesting of RSUs       55 years  
Threshold years required for retirement age       70 years  
Non Executive Employee [Member] | Minimum [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       3 years  
Non Executive Employee [Member] | Maximum [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       4 years  
Non Executive Employee [Member] | Restricted Stock Units (RSUs) [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       3 years  
Directors [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       1 year  
Directors [Member] | Restricted Stock Units (RSUs) [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       1 year  
Executives [Member] | Performance Shares [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Options granted 130,000        
Stock options cancelled     50,000    
Executives [Member] | Service-Based Stock Options [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Options granted     80,000    
2015 ESPP [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Percentage related to employees to purchase shares at the lower fair market value at offering period       85.00%