Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Share-based Compensation (Details)

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Summary of Significant Accounting Policies - Share-based Compensation (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Jan. 01, 2017
Accounting Policies [Abstract]      
Stock-based compensation expense $ 355 $ 343  
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested stock options unrecognized compensation expense $ 3,594    
Non-vested stock options unrecognized compensation expense, weighted-average period of recognition 2 years 6 months    
Accounting Standards Update 2016-09      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Deferred income tax assets, net     $ 4,000
Retained Earnings | Accounting Standards Update 2016-09      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Credit to retained earnings   $ 4,000