Quarterly report pursuant to Section 13 or 15(d)

Stock-based Compensation - Additional Information (Details)

v3.10.0.1
Stock-based Compensation - Additional Information (Details) - USD ($)
 1 Months Ended 3 Months Ended 6 Months Ended
Dec. 31, 2017
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2018
Jun. 30, 2017
Additional disclosures [Abstract]          
Stock-based compensation expense       $ 2,186,000 $ 2,855,000
Stock Options [Member]          
Additional disclosures [Abstract]          
Minimum age required for employees to qualify for immediate vesting of RSUs       55 years  
Threshold years required for retirement age       70 years  
Unrecognized compensation expense related to stock options   $ 6,400,000   $ 6,400,000  
Weighted average period of unrecognized compensation expense expected to be recognized       2 years  
Options outstanding 1,622,065 1,607,932   1,607,932  
Options granted       233,208  
Performance Shares [Member]          
Additional disclosures [Abstract]          
Unrecognized compensation expense related to stock options   $ 300,000   $ 300,000  
Options outstanding   82,500   82,500  
Number of options subject to achievement of corporate goals   41,250   41,250  
Stock-based compensation expense   $ 55,000   $ 100,000  
Grant date fair value   400,000   $ 400,000  
Restricted Stock Units (RSUs) [Member]          
Additional disclosures [Abstract]          
Minimum age required for employees to qualify for immediate vesting of RSUs       55 years  
Threshold years required for retirement age       70 years  
Weighted average period of unrecognized compensation expense expected to be recognized       1 year 3 months 18 days  
Unrecognized compensation expense related to employee RSUs   $ 4,000   $ 4,000  
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]          
Additional disclosures [Abstract]          
Options granted 130,000        
Stock options cancelled     50,000    
Executives [Member] | Service-Based Stock Options [Member]          
Additional disclosures [Abstract]          
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%