Debt - Convertible Notes (Details)		3 Months Ended		6 Months Ended
	Feb. 14, 2014 USD ($)	Jun. 30, 2016 USD ($) $ / shares	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) item $ / shares	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Liability component:
Net carrying amount		$ 174,953,000		$ 174,953,000		$ 170,749,000
Total interest expense recognized
Total interest expense		$ 18,250,000	$ 10,205,000	$ 36,693,000	$ 20,572,000
Convertible 2.5% notes
Debt
Aggregate principal amount of debt issued	$ 200,000,000
Net proceeds from issuance of convertible debt	193,300,000
Debt issuance costs	6,700,000
Proceeds used to pay the cost of the bond hedges (after such cost was partially offset by proceeds from the sale of warrants)	14,100,000
Interest rate (as a percent)		2.50%		2.50%
Initial conversion rate of common stock per $1000 of principal amount of Notes (in shares)				36.9079
Principal amount used for debt instrument conversion ratio		$ 1,000		$ 1,000
Initial conversion price of convertible notes into common stock (in dollars per share) | $ / shares		$ 27.09		$ 27.09
Number of consecutive trading days during which the closing price of the entity's common stock must exceed or equal the conversion price for at least 20 days in order for the notes to be convertible				30 days
Period of amortization of debt discount to interest expense using effective interest method				5 years
Debt term				5 years
Effective interest rate on liability component		7.23%		7.23%
Liability component:
Principal		$ 199,998,000		$ 199,998,000
Less: debt discount, net		(25,045,000)		(25,045,000)
Net carrying amount		174,953,000		174,953,000
Equity component		38,188,000		38,188,000
Debt issuance costs allocated to equity component	1,300,000
Debt issuance costs allocated to the liability component	$ 5,400,000
Total interest expense recognized
Contractual interest expense		1,250,000	1,250,000	2,500,000	2,500,000
Amortization of debt issuance costs		265,000	246,000	524,000	480,000
Amortization of debt discount		1,867,000	1,727,000	3,682,000	3,376,000
Total interest expense		3,382,000	$ 3,223,000	$ 6,706,000	$ 6,356,000
Convertible 2.5% notes | Debt Instrument Convertible Covenant One
Debt
Number of days during 30 consecutive trading days in which the closing price of the entity's common stock must exceed or equal the conversion price for the notes to be convertible | item				20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed or equal the conversion price for at least 20 days in order for the notes to be convertible				30 days
Convertible 2.5% notes | Debt Instrument Convertible Covenant One | Minimum
Debt
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed or be equal in order for the notes to be convertible				130.00%
Convertible 2.5% notes | Debt Instrument Convertible Covenant Two
Debt
Principal amount used for debt instrument conversion ratio		1,000		$ 1,000
Number of consecutive business days after any five consecutive trading day period during the note measurement period				5 days
Number of consecutive trading days before five consecutive business days during the note measurement period				5 days
Convertible 2.5% notes | Debt Instrument Convertible Covenant Two | Maximum
Debt
Percentage of product of the last reported sale price of the entity's common stock and the conversion rate of convertible debt instruments				98.00%
Convertible 2.5% notes | Debt Instrument Convertible Covenant Three
Debt
Principal amount used for debt instrument conversion ratio		1,000		$ 1,000
2.5 Percent Convertible Notes
Debt
Aggregate principal amount of debt issued		$ 200,000,000		$ 200,000,000
Interest rate (as a percent)		2.50%		2.50%		2.50%