Long-Term Debt - Convertible Senior Notes Due 2032 (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 20, 2018	Mar. 31, 2012	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	May 04, 2018
Debt Instrument [Line Items]
Principal amount			$ 459,224		$ 459,224
Repurchase of convertible debt					0	$ 60,362
Loss on extinguishment of long-term debt			$ (18)	$ (76)	$ (18)	$ (1,181)
Convertible Senior Notes Maturing March 2032 (Redeemed May 2018)
Debt Instrument [Line Items]
Principal amount		$ 200,000
Interest rate (as a percent)		3.25%
Maturity date		Mar. 15, 2032
Repurchased principal amount	$ 59,300						$ 800
Repurchase of convertible debt	59,500
Payments for fees	200
Loss on extinguishment of long-term debt	$ (200)