Annual report pursuant to Section 13 and 15(d)

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

v3.3.1.900
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, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of Employee Stock Purchase Plan (ESPP) Disclosures [Line Items]      
Share-based compensation $ 7,486 $ 6,681 $ 6,178
Employee Stock Purchase Plan [Member]      
Schedule of Employee Stock Purchase Plan (ESPP) Disclosures [Line Items]      
Number of shares authorized under the plan 392,987    
Common stock issued under employee stock purchase plan (in shares) 10,805 8,530 8,800
Weighted average price of shares purchased (dollars per share) $ 41.55 $ 41.51 $ 33.68
Purchase Period for Employee Stock Purchase Plan 6 months    
Weighted Average Grant Date Fair Value $ 5.82 $ 7.74 $ 7.52
Share-based compensation $ 61 $ 66 $ 66