Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity Stock Options and Net Income per Share - Employee Stock Purchase Plan (Details)

v3.10.0.1
Shareholders' Equity Stock Options and Net Income per Share - Employee Stock Purchase Plan (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Schedule of Employee Stock Purchase Plan (ESPP) Disclosures [Line Items]      
Share-based compensation $ 10,549 $ 8,103 $ 8,334
Employee Stock Purchase Plan [Member]      
Schedule of Employee Stock Purchase Plan (ESPP) Disclosures [Line Items]      
Number of shares authorized under the plan 362,404    
Common stock issued under employee stock purchase plan (in shares) 9,455 9,954 11,174
Weighted average price of shares purchased (dollars per share) $ 50.63 $ 46.01 $ 39.50
Purchase Period for Employee Stock Purchase Plan 6 months    
Weighted Average Grant Date Fair Value $ 6.26 $ 9.26 $ 6.46
Share-based compensation $ 59 $ 92 $ 72