Long-Term Debt - Convertible Senior Notes Due 2032 (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2012	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Nov. 01, 2016	Jul. 31, 2016	Jun. 30, 2016
Debt Instrument [Line Items]
Principal amount		$ 530,508		$ 530,508
Gain (loss) on early extinguishment of long-term debt		0	$ 244	(397)	$ 546
Unamortized debt discount		15,607		15,607
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Principal amount	$ 200,000	60,115		60,115		$ 60,115
Interest rate (as a percent)	3.25%
Frequency of periodic payment	semi-annually
Maturity date	Mar. 15, 2032
Initial conversion ratio	0.0399752
Initial conversion price per share (in dollars per share)	$ 25.02
Redemption price as a percentage of principal amount	100.00%
Repurchase price as a percentage of principal amount	100.00%
Repurchased principal amount							$ 125,000	$ 7,600	$ 7,300
Gain (loss) on early extinguishment of long-term debt			$ 200		$ 500
Expected life used to estimate fair value	6 years
Effective interest rate (as a percent)	6.90%
Carrying amount of equity component	$ 22,500
Unamortized debt discount	$ 35,400	$ 1,052		$ 1,052		$ 2,600