Short and Long-term Funding FHLB Maturity Schedule (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 3,574,371	$ 3,184,168
Weighted Average Coupon Rate	2.19%	1.26%
Maturity or put date 1 year or less
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 2,262,584	$ 2,434,000
Weighted Average Coupon Rate	2.06%	1.26%
After 1 but within 2
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 1,285,039	$ 750,013
Weighted Average Coupon Rate	2.39%	1.23%
After 2 but within 3
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 14,393	$ 155
Weighted Average Coupon Rate	2.98%	4.91%
After 3 years
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 12,354	$ 0
Weighted Average Coupon Rate	4.55%	0.00%