Debt - Convertible Notes (Details)					3 Months Ended		6 Months Ended
	Jun. 07, 2017 USD ($)	May 10, 2017 USD ($)	May 05, 2017 USD ($)	Feb. 14, 2014 USD ($)	Jun. 30, 2017 USD ($) $ / shares	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) day $ / shares	Jun. 30, 2016 USD ($)
Debt Instrument [Line Items]
Payment of convertible debt issuance costs							$ 9,553,000	$ 0
Repurchase price of convertible debt							170,371,000	0
Gain (loss) on debt extinguishment					$ (9,516,000)	$ 0	$ (9,516,000)	$ 0
Convertible Notes
Debt Instrument [Line Items]
Period of amortization of debt discount to interest expense using effective interest method (in years)							5 years
Net proceeds from issuance of convertible debt				$ 193,300,000
Debt issuance costs				6,700,000
Interest rate					2.50%		2.50%
Initial conversion rate of common stock per $1000 of principal amount							0.0369079
Initial conversion price of convertible notes into common stock (in usd per share) | $ / shares					$ 27.09		$ 27.09
Consecutive trading period (in days)							30 days
Principal amount used for debt instrument conversion ratio					$ 1,000		$ 1,000
Effective interest rate on liability component (as a percent)					7.79%		7.79%
Proceeds used to pay the cost of the bond hedges				14,100,000
Convertible Notes | Debt Instrument Convertible Covenant One
Debt Instrument [Line Items]
Trading period (in days) | day							20
Consecutive trading period (in days)							30 days
Convertible Notes | Debt Instrument Convertible Covenant One | Minimum
Debt Instrument [Line Items]
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 (as a percent)							130.00%
Convertible Notes | Debt Instrument Convertible Covenant Two
Debt Instrument [Line Items]
Consecutive business days after any five consecutive trading day period during the note measurement period (in days)							5 days
Consecutive trading days before five consecutive business days during the note measurement period (in days)							5 days
Principal amount used for debt instrument conversion ratio					$ 1,000		$ 1,000
Convertible Notes | Debt Instrument Convertible Covenant Two | Maximum
Debt Instrument [Line Items]
Product of the last reported sale price of the entity's common stock and the conversion rate of convertible debt instruments (less than) (as a percent)							98.00%
Convertible Notes due 2022
Debt Instrument [Line Items]
Aggregate principal amount of debt issued	$ 20,000,000	$ 300,000,000
Interest rate					3.25%		3.25%
Debt term (in years)							5 years
Convertible Notes due 2022 | Convertible Notes
Debt Instrument [Line Items]
Period of amortization of debt discount to interest expense using effective interest method (in years)							5 years
Net proceeds from issuance of convertible debt	19,400,000	291,000,000
Payment of convertible debt issuance costs	600,000	$ 9,000,000
Debt issuance costs	$ 9,600,000				$ 9,600,000		$ 9,600,000
Debt issuance costs, allocated to equity component							2,200,000
Debt issuance costs allocated to the liability component							$ 7,400,000
Interest rate					3.25%		3.25%
Initial conversion rate of common stock per $1000 of principal amount							0.0365464
Initial conversion price of convertible notes into common stock (in usd per share) | $ / shares					$ 27.36		$ 27.36
Effective interest rate on liability component (as a percent)					9.49%		9.49%
Convertible Notes due 2019
Debt Instrument [Line Items]
Aggregate principal amount of debt issued				$ 200,000,000
Interest rate					2.25%		2.25%
Convertible Notes due 2019 | Convertible Notes
Debt Instrument [Line Items]
Repurchase of principal amount of convertible debt			$ 158,900,000
Repurchase price of convertible debt			$ 171,300,000
Gain (loss) on debt extinguishment							$ 200,000