Borrowings - Summary of Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amount
Total borrowings, net	$ 3,634,752	$ 3,964,222
Weighted Average Rate
Total debt (as a percent)	2.56%	2.40%
Securities sold under agreements to repurchase
Amount
Securities sold under agreements to repurchase	$ 1,100,000	$ 1,100,000	$ 1,100,000
Weighted Average Rate
Long-term debt (as a percent)	3.62%	3.62%	3.62%
FHLB-NY advances | Federal Home Loan Bank of New York
Amount
FHLB-NY advances	$ 2,090,000	$ 2,180,000	$ 2,384,000
Weighted Average Rate
Long-term debt (as a percent)	1.88%	1.86%	1.72%
Other borrowings, net
Amount
Other borrowings, net	$ 249,752	$ 249,222
Weighted Average Rate
Long-term debt (as a percent)	5.00%	5.00%
Federal funds purchased
Amount
Federal funds purchased	$ 195,000	$ 435,000
Weighted Average Rate
Short-term debt (as a percent)	0.81%	0.57%