Convertible Senior Notes - Additional Information (Details) - Notes $ / shares in Units, $ in Thousands		6 Months Ended
	Jun. 17, 2014 USD ($)	Jun. 30, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Interest rate (as a percent)	1.75%
Net proceeds from offering, after deducting Underwriter's discount and estimated offering expenses payable	$ 337,500
Principal	$ 345,000	$ 345,000	$ 345,000
Notes maturity date		Jun. 15, 2021
Notes frequency of periodic payment		semiannually in arrears in cash
Period to comply with covenants		270 days
Debt issuance costs		$ 7,500
Debt issuance costs allocated to equity component		1,300
Debt issuance costs allocated to liability component		$ 6,200
Remaining contractual life		3 years
Effective interest rate on liability component (as a percent)		4.80%
Debt Conversion Terms upon Occurrence of Certain Fundamental Company Changes
Debt Instrument [Line Items]
Principal amount of Notes or an integral multiple thereof in which holder may repurchase the Notes		$ 1,000
Debt Conversion Event Term
Debt Instrument [Line Items]
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable		25.00%
In event of default arising out of certain bankruptcy events, percentage of principal amount due and payable		100.00%
Convertible Debt Holder
Debt Instrument [Line Items]
Initial conversion rate of common stock		23.4968
Initial conversion price of convertible notes into common stock (in dollars per share) | $ / shares		$ 42.56