Convertible Senior Notes - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended
	Jan. 03, 2012	Nov. 30, 2009	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Debt discount		$ 13,700,000	$ 13,700,000
4.50% Convertible senior notes (due 2014)
Debt Instrument [Line Items]
Long term debt, face amount		100,000,000	100,000,000	100,000,000
Debt instrument, interest rate		4.50%	4.50%	4.50%
Frequency of interest payment		Semi-annually
Debt instrument, maturity date		Nov. 01, 2014	Nov. 01, 2014
Conversion rate in share per $1000 principal amount of notes		63.2091
Debt instrument, conversion rate		$ 15.82
Cash dividend on common stock per share paid	$ 0.10
Debt instrument, effective interest rate			7.90%
Debt issuance costs			$ 3,700,000
Debt issuance costs, amortization period			5 years
4.50% Convertible senior notes (due 2014) | Scenario, Forecast
Debt Instrument [Line Items]
Conversion rate in share per $1000 principal amount of notes		67.9486
Debt instrument, conversion rate		$ 14.72