Convertible Senior Notes - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt Disclosure [Abstract]
Amortization of debt discount and issuance costs	$ 5,731	$ 5,534	$ 17,044	$ 16,457
Capitalization of interest expense	(985)	(868)	(3,055)	(2,499)
Total interest expense	$ 4,746	$ 4,666	$ 13,989	$ 13,958