Interest Expense Related to Notes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Coupon interest at 1.25%									$ 16,284	$ 16,020	$ 14,703
Amortization of discounts and debt issuance costs									13,679	13,277	9,451
Total interest expense	$ 7,403	$ 9,254	$ 7,483	$ 7,256	$ 7,292	$ 7,542	$ 7,230	$ 7,233	31,396	29,297	28,055
1.25% Cash Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Coupon interest at 1.25%									4,312	4,312	2,312
Amortization of discounts and debt issuance costs									11,994	11,433	5,910
Total interest expense									$ 16,306	$ 15,745	$ 8,222