Components of Current and Deferred Income Tax Expense (Benefit) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current income tax expense (benefit):
Federal and foreign									$ 39,242	$ 573	$ 11,965
State and local									146	340	97
Subtotal									39,388	913	12,062
Deferred income tax expense (benefit):
Federal and foreign									(11,414)	6,224	17,189
State and local
Subtotal									(11,414)	6,224	17,189
Income tax expense (benefit)	$ 13,243	$ 5,225	$ 6,225	$ 3,281	$ 2,122	$ 4,476	$ 5,032	$ (4,493)	$ 27,974	$ 7,137	$ 29,251