Components of Convertible Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Apr. 30, 2009	Apr. 06, 2009
Debt Instrument
Debt principal	$ 190,000	$ 190,000	$ 190,000	$ 190,000
Unamortized discount	20,104	33,902
Net carrying amount of the convertible debt	169,896	156,098
Contractual interest expense on the coupon	8,550	8,550
Amortization of the discount component and debt issue fees recognized as interest expense	14,612	12,853
Total interest expense on the convertible debt	$ 23,162	$ 21,403