Key Components of Convertible Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Convertible senior notes, net	$ 100,000	$ 94,918
4.50% Convertible senior notes (due 2014)
Debt Instrument [Line Items]
Principal amount of notes	39,000	100,000
Unamortized equity component	(902)	(5,082)
Convertible senior notes, net	38,098	94,918
Contractual interest expense on the coupon	3,356	4,500	4,500
Amortization of debt discount and debt issuance costs recognized as interest expense	2,030	3,468	3,466
Amortization of Deferred Charges, Total	5,386	7,968	7,966
4.25% Convertible Senior Notes (due 2018)
Debt Instrument [Line Items]
Principal amount of notes	100,000
Contractual interest expense	1,771
Convertible senior notes, net	100,000
Amortization of Deferred Charges, Total	$ 1,771