Long-Term Debt - Convertible Senior Notes Due 2032 (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2016	Mar. 31, 2012	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Nov. 01, 2016	Jul. 31, 2016
Debt Instrument [Line Items]
Principal amount			$ 543,835		$ 543,835
Gain (loss) on early extinguishment of long-term debt			(397)	$ 302	(397)	$ 302
Unamortized debt discount			16,791		16,791
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	$ 7,300			$ 7,300		$ 7,300		$ 125,000	$ 7,600
Gain (loss) on early extinguishment of long-term debt	$ 300
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	$ 1,573		$ 1,573		$ 2,600