Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Share-Based Payments Share-Based Payments - Employee Stock Purchase Plan (Details)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
$ / shares
shares
Jun. 30, 2017
USD ($)
$ / shares
Jun. 30, 2018
USD ($)
$ / shares
shares
Jun. 30, 2017
USD ($)
$ / shares
shares
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]        
Share-based compensation expense | $ $ 2,417 $ 2,064 $ 4,678 $ 4,026
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 367,309   367,309  
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     4,550 5,188
Share-based Compensation Arrangement by Share-based Payment Award, Per Share Weighted Average Price of Shares Purchased (in dollars per share) | $ / shares $ 51.98 $ 43.59 $ 51.98 $ 43.59
Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares     $ 7.10 $ 9.69
Share-based compensation expense | $     $ 32 $ 51