Long-Term Debt - Convertible Senior Notes Due 2022 (Details) $ / shares in Units, $ in Thousands		1 Months Ended
	Nov. 01, 2016 USD ($) $ / shares	Mar. 31, 2012 USD ($) $ / shares	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Debt Instrument [Line Items]
Principal amount			$ 530,508
Unamortized debt discount			15,607
Convertible Senior Notes Maturing May 2022 [Member]
Debt Instrument [Line Items]
Principal amount	$ 125,000		125,000	$ 125,000
Net proceeds from debt issuance	$ 121,700
Interest rate (as a percent)	4.25%
Frequency of periodic payment	semi-annually
Maturity date	May 01, 2022
Initial conversion ratio	0.0719748
Initial conversion price per share (in dollars per share) | $ / shares	$ 13.89
Redemption price as a percentage of principal amount	100.00%
Minimum percentage in aggregate principal amount	25.00%
Unamortized debt discount	$ 16,900		14,555	16,500
Expected life used to estimate fair value	5 years 6 months
Effective interest rate (as a percent)	7.30%
Carrying amount of equity component	$ 11,000
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Principal amount		$ 200,000	60,115	60,115
Repurchased principal amount	$ 125,000				$ 7,600	$ 7,300
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) | $ / shares		$ 25.02
Redemption price as a percentage of principal amount		100.00%
Unamortized debt discount		$ 35,400	$ 1,052	$ 2,600
Expected life used to estimate fair value		6 years
Effective interest rate (as a percent)		6.90%
Carrying amount of equity component		$ 22,500