Convertible Senior Notes (Due 2022) (Details)	1 Months Ended	3 Months Ended
	Jan. 31, 2015 USD ($) d $ / shares	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Interest expense
Amortization of debt discount		$ 6,973,000	$ 6,300,000
Senior Notes | Convertible Senior Notes Due 2022
Debt Instrument [Line Items]
Principal	$ 400,000,000	400,000,000		$ 400,000,000
Interest rate	2.50%
Proceeds from offering	$ 387,200,000
Trading days | d	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	$ 400,000,000	400,000,000		400,000,000
Less: Debt discount, net		(72,568,000)		(75,754,000)
Net carrying amount		$ 327,432,000		$ 324,246,000
Remaining contractual life		4 years 9 months 18 days
Interest expense
Contractual interest expense		$ 2,500,000	2,500,000
Amortization of debt discount		3,187,000	2,974,000
Total		$ 5,687,000	$ 5,474,000
Effective interest rate of the liability component		6.50%	6.50%
Significant Other Observable Inputs (Level 2) | Senior Notes | Convertible Senior Notes Due 2022
Liability component
Fair value of Notes		$ 631,900,000