Summary of Interest Expense on Debt (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Interest Expenses [Line Items]
Total interest expense on convertible debt	$ 39,499	$ 38,244	$ 36,642
Convertible Senior Notes
Schedule Of Interest Expenses [Line Items]
Coupon interest	9,555	9,750	9,417
Amortization of issuance costs	3,367	3,294	3,332
Accretion of discount on convertible notes	26,577	25,200	23,893
Total interest expense on convertible debt	$ 39,499	$ 38,244	$ 36,642