Borrowings (Details 5) (FHLB advances, FHLB-NY, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
FHLB advances | FHLB-NY
FHLB-NY advances
Average balance during the year	$ 2,332,718	$ 2,512,425	$ 2,765,985
Maximum balance at any month end during the year	2,617,000	2,881,000	3,215,000
Balance outstanding at end of year	$ 2,384,000	$ 2,454,000	$ 2,897,000
Weighted average interest rate during the year (as a percent)	1.78%	2.00%	2.24%
Weighted average interest rate at end of year	1.72%	1.79%	2.07%