Convertible Senior Notes - Components of Total Interest Expense, Net Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
Contractual coupon interest expense	$ 3,288	$ 3,300	$ 3,300
Amortization of debt issuance costs	696	662	599
Accretion of debt discount	5,710	5,250	4,818
Total	$ 9,694	$ 9,212	$ 8,717
Effective interest rate	8.65%	8.66%	8.66%