Key Components of Convertible Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Nov. 30, 2009
Debt Instrument [Line Items]
Convertible senior notes, net	$ 94,918	$ 92,188
4.50% Convertible senior notes (due 2014)
Debt Instrument [Line Items]
Principal amount of notes	100,000	100,000		100,000
Unamortized equity component	(5,082)	(7,812)
Convertible senior notes, net	94,918	92,188
Contractual interest expense on the coupon	4,500	4,500	4,500
Amortization of equity component and debt issuance costs recognized as interest expense	3,468	3,466	3,466
Amortization of Deferred Charges, Total	$ 7,968	$ 7,966	$ 7,966