Liabilities - Convertible Senior Notes (Details) $ / shares in Units, $ in Thousands		3 Months Ended
	Jan. 10, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($)
Long-term debt
Proceeds received, net of transaction fees		$ 335,752
Convertible Senior Notes
Long-term debt
Aggregate principal amount	$ 345,000	345,000
Interest rate (as a percent)	2.70%
Proceeds received, net of transaction fees	$ 335,800
Conversion rate of the Notes to common stock, per $1,000 principal amount of Notes	24.9800
Initial conversion price per share of common stock | $ / shares	$ 40.03
Threshold trading days for convertible debt	20 days
Threshold consecutive trading days for convertible debt	30 days
Number of consecutive business days after the measurement period	5 days
Number of consecutive trading days making up the measurement period	5 days
Percentage of minimum stock price trigger for conversion	130.00%
Maximum calculated percentage to which trading price of notes is compared in order to trigger conversion feature of notes	98.00%
Fair value inputs discount rate (as a percent)	7.00%
Unamortized debt discount	$ (72,500)	(70,527)
Transaction costs	$ 9,200
Unamortized transaction costs		(7,104)
Net carrying value		267,369
Cash Interest Expense
Coupon interest expense		1,915
Non-Cash Interest Expense
Amortization of debt discount		1,985
Amortization of transaction costs		200
Total Interest Expense		4,100
Convertible Senior Notes | Level 2
Non-Cash Interest Expense
Estimated fair value of Convertible Senior Notes		$ 361,300