Borrowings - Summary of FHLB-NY Advances (Details) - FHLB-NY advances - Federal Home Loan Bank of New York - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
FHLB-NY advances
Average balance during the year	$ 2,250,592	$ 2,332,718	$ 2,512,425
Maximum balance at any month end during the year	2,515,000	2,617,000	2,881,000
Balance outstanding at end of year	$ 2,180,000	$ 2,384,000	$ 2,454,000
Weighted average interest rate during the year	1.79%	1.78%	2.00%
Weighted average interest rate at end of year	1.86%	1.72%	1.79%