Short and Long-Term Funding FHLB Maturity Schedule (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 2,944,769	$ 3,574,371
FHLB Weighted Average Coupon Rate	2.71%	2.19%
FHLB Maturity within One Year [Domain]
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 2,232,703	$ 2,262,584
FHLB Weighted Average Coupon Rate	2.79%	2.06%
FHLB Maturity One Year to Two Years [Domain]
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 688,035	$ 1,285,039
FHLB Weighted Average Coupon Rate	2.43%	2.39%
FHLB Maturity Over Two Years to Three Years [Domain]
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 16,064	$ 14,393
FHLB Weighted Average Coupon Rate	3.22%	2.98%
FHLB Maturity Over Three Years [Domain]
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 7,968	$ 12,354
FHLB Weighted Average Coupon Rate	3.78%	4.55%