Borrowings - Summary of Information Relating to FHLB-NY Advances (Details) - FHLB-NY advances - Federal Home Loan Bank of New York - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Average balance during the year	$ 2,206,074	$ 2,250,592	$ 2,332,718
Maximum balance at any month end during the year	2,374,000	2,515,000	2,617,000
Balance outstanding at end of year	$ 2,090,000	$ 2,180,000	$ 2,384,000
Weighted average interest rate during the year	1.83%	1.79%	1.78%
Weighted average interest rate at end of year	1.88%	1.86%	1.72%