Convertible Senior Notes - Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	9 Months Ended
	Jun. 30, 2016	Jun. 30, 2012	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Settlement of warrants				$ 0	$ 87,874
Senior Notes | Convertible Senior Notes Due 2017
Debt Instrument [Line Items]
Debt, aggregate principal amount repurchased	$ 220,000
2017 Warrants
Debt Instrument [Line Items]
Proceeds from sale of warrants		$ 38,400
Settlement of warrants	$ 87,900
Common stock exercisable upon conversion (in shares)		2,000,000
Exercise price of warrants (in dollars per share)		$ 34.20
Warrants exercised (in shares)			443,070
Common stock, shares, issued (in shares)			24,217
Warrants outstanding (in shares)			1,427,679	1,427,679