Convertible Senior Notes (Due 2022) (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2015 USD ($) d $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Interest expense
Amortization of debt discount				$ 19,392,000	$ 17,532,000
Senior Notes [Member] | Convertible Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Principal	$ 400,000,000	$ 400,000,000		400,000,000		$ 400,000,000
Interest rate	2.50%
Proceeds from offering	$ 387,200,000
Trading period | 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 of equity component		54,300,000		54,300,000
Net deferred tax liabilities	$ 31,800,000
Liability component
Principal	$ 400,000,000	400,000,000		400,000,000		400,000,000
Less: Debt discount, net		(78,850,000)		(78,850,000)		(87,893,000)
Net carrying amount		321,150,000		321,150,000		$ 312,107,000
Fair value of Notes		350,900,000		$ 350,900,000
Remaining contractual life				5 years 3 months 15 days
Interest expense
Contractual interest expense		2,500,000	$ 2,505,000	$ 7,500,000	7,139,000
Amortization of debt discount		3,078,000	2,878,000	9,043,000	8,053,000
Total		$ 5,578,000	$ 5,383,000	$ 16,543,000	$ 15,192,000
Effective interest rate of the liability component		6.50%	6.50%	6.50%	6.50%