Borrowings (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
FHLB-NY advances
Balance outstanding at end of year	$ 2,897,000	$ 2,043,000
Weighted average interest rate at end of year (as a percent)	3.03%	3.98%
FHLB Advances | FHLB-NY
FHLB-NY advances
Average balance during the year	2,765,985	2,063,700	2,915,658
Maximum balance at any month end during the year	3,215,000	2,487,000	3,235,000
Balance outstanding at end of year	$ 2,897,000	$ 2,043,000	$ 2,391,000
Weighted average interest rate during the year (as a percent)	2.24%	3.45%	3.67%
Weighted average interest rate at end of year (as a percent)	2.07%	3.13%	3.62%