Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments Share-Based Payments - Employee Stock Purchase Plan (Details)

v3.7.0.1
Share-Based Payments Share-Based Payments - Employee Stock Purchase Plan (Details)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
USD ($)
$ / shares
shares
Jun. 30, 2016
USD ($)
$ / shares
Jun. 30, 2017
USD ($)
$ / shares
shares
Jun. 30, 2016
USD ($)
$ / shares
shares
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]        
Share-based compensation expense | $ $ 2,064 $ 2,159 $ 4,026 $ 4,111
Employee Stock Purchase Plan [Member]        
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]        
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares) | shares 376,625   376,625  
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date     90.00%  
Number of Large Lump Sum Contributions Related to ESPP Stock Purchases 2   2  
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares) | shares     5,188 5,592
Share-based Compensation Arrangement by Share-based Payment Award, Per Share Weighted Average Price of Shares Purchased (in dollars per share) | $ / shares $ 43.59 $ 38.50 $ 43.59 $ 38.50
Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares     $ 9.69 $ 6.03
Share-based compensation expense | $     $ 51 $ 34