Income taxes - Components of Income Tax Expense (Benefit) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current
Federal	$ 309,156	$ 277,631	$ 250,489
State and city	82,014	53,566	55,071
Total current	391,170	331,197	305,560
Deferred
Federal	117,229	34,325	47,123
State and city	14,629	(401)	3,945
Total deferred	131,858	33,924	51,068
Income taxes	$ 523,028	$ 365,121	$ 356,628