Interest Expense Related to 1.25% Notes (Detail) - 1.25% Cash Convertible Senior Notes [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Instrument [Line Items]
Coupon interest at 1.25%	$ 1,078	$ 1,078	$ 2,156	$ 2,156
Amortization of discounts and debt issuance costs	3,278	3,108	6,524	6,216
Total interest expense related to the 1.25% Notes	$ 4,356	$ 4,186	$ 8,680	$ 8,372