Convertible and Long-term Debt Obligations - Schedule of Interest Incurred (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Disclosure [Abstract]
Contractual interest coupon	$ 10,588	$ 11,256	$ 21,136	$ 17,407
Amortization of debt issuance costs	1,642	2,207	3,257	3,515
Amortization of debt discounts	30,525	30,002	60,384	53,964
Total	$ 42,755	$ 43,465	$ 84,777	$ 74,886