Convertible Senior Notes - Due 2022 (Details)		3 Months Ended		9 Months Ended
	Mar. 31, 2015 USD ($) day $ / shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Interest expense
Amortization of debt discount				$ 20,325,000	$ 19,392,000
Senior Notes | Convertible Senior Notes Due 2022
Debt Instrument [Line Items]
Interest rate	2.50%
Proceeds from offering	$ 387,200,000
Trading days | day	20
Redemption consecutive trading period	30 days
Redemption stock price conversion threshold (greater than or equal to)	130.00%
Consecutive measurement period	5 days
Percent of trading price (less than)	98.00%
Conversion ratio				0.0298806
Conversion price (USD per share) | $ / shares	$ 33.47
Redemption trading period	19 days
Percent of principal amount plus accrued and unpaid interest	100.00%
Debt default principal amount percentage	25.00%
Debt instrument, term	7 years
Carrying amount, equity component	$ 88,900,000
Net deferred tax liabilities	$ 31,800,000
Liability component
Principal		$ 399,997,000		$ 399,997,000		$ 400,000,000
Less: Debt discount, net		(66,064,000)		(66,064,000)		(75,754,000)
Net carrying amount		333,933,000		$ 333,933,000		$ 324,246,000
Remaining contractual life				4 years 3 months 18 days
Interest expense
Contractual interest expense		2,500,000	$ 2,500,000	$ 7,500,000	7,500,000
Amortization of debt discount		3,298,000	3,078,000	9,690,000	9,043,000
Total		$ 5,798,000	$ 5,578,000	$ 17,190,000	$ 16,543,000
Effective interest rate of the liability component		6.50%	6.50%	6.50%	6.50%
Senior Notes | Convertible Senior Notes Due 2022 | Significant Other Observable Inputs (Level 2)
Liability component
Fair value of Notes		$ 504,700,000		$ 504,700,000