Senior Notes Due May 1, 2016 - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended		9 Months Ended
	Apr. 30, 2009	Apr. 17, 2006	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Debt Instrument [Line Items]
Senior Notes			$ 114,386,000		$ 114,386,000		$ 114,276,000
Senior Notes due May 1, 2016
Debt Instrument [Line Items]
Principal amount of senior notes		125,000,000
Interest rate stated on senior notes		7.00%
Senior notes due date		May 01, 2016
Net proceeds from issuance of senior notes		123,500,000
Aggregate principal amount of senior notes repurchased from unaffiliated note holder	10,000,000
Repurchased senior notes	7,000,000
Pretax gain from repurchase of senior notes	3,000,000
Outstanding principal amount of senior notes			114,400,000		114,400,000
Unamortized discount			600,000		600,000
Senior Notes			115,000,000		115,000,000
Fair value of senior notes			121,000,000		121,000,000		119,300,000
Interest expense on senior notes			$ 2,100,000	$ 6,100,000	$ 2,100,000	$ 6,100,000
Effective interest rate related to senior notes			7.17%		7.17%
Debt instrument, covenant compliance					As of September 30, 2012, the Company was in compliance with all such covenants.
Senior Notes due May 1, 2016 | Semi Annual Payment, First Payment
Debt Instrument [Line Items]
Interest payment date on senior notes			--05-01		--05-01
Senior Notes due May 1, 2016 | Semi Annual Payment, Second Payment
Debt Instrument [Line Items]
Interest payment date on senior notes			--11-01		--11-01