Quarterly report pursuant to Section 13 or 15(d)

Debt (Conv) (Details)

v3.8.0.1
Debt (Conv) (Details) - Convertible Notes
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Dec. 15, 2014
USD ($)
item
$ / shares
Sep. 30, 2017
USD ($)
$ / shares
Sep. 30, 2016
USD ($)
Sep. 30, 2017
USD ($)
$ / shares
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Debt            
Face amount $ 172,500 $ 172,500   $ 172,500   $ 172,500
Net proceeds from offering $ 166,967          
Interest rate (as a percent) 1.75%          
Repurchase percentage of principal (as a percent) 100.00%          
Conversion rate 15.9022          
Principal amount | $ / shares $ 1          
Conversion price (in dollars per share) | $ / shares $ 62.88 $ 62.88   $ 62.88    
Threshold trading days (in days) | item 20          
Consecutive trading days | item 30          
Threshold percentage of stock price trigger (as a percent) 130.00%          
Threshold business days 5 days          
Threshold consecutive trading-day period 5 days          
Threshold percentage of trading price trigger (as a percent) 98.00%          
Allocated to equity components $ 26,618          
Offering costs 882          
Discount $ 27,500 $ 13,075   $ 13,075   $ 17,149
Accretion of debt discount   $ 1,393 $ 1,323 $ 4,074 $ 3,901  
Effective interest rate (as a percent)   5.40% 6.00%   6.00%