Mortgage Servicing Rights (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Data and key economic assumptions related to mortgage servicing rights
Unpaid principal balance	$ 4,012,519	$ 2,763,344	$ 3,090,839
Weighted-average prepayment speed (CPR)	8.04%	7.34%	8.89%
Estimated impact of a 10% increase	$ (1,592)	$ (1,034)	$ (1,203)
Estimated impact of a 20% increase	$ (3,095)	$ (2,010)	$ (2,330)
Discount rate	9.69%	9.64%	9.51%
Estimated impact of a 100bp increase	$ (2,027)	$ (1,368)	$ (1,357)
Estimated impact of a 200bp increase	$ (3,896)	$ (2,629)	$ (2,612)
Weighted-average coupon interest rate	3.89%	3.83%	3.97%
Weighted-average servicing fee (basis points)	0.2636%	0.2587%	0.2504%
Weighted-average remaining maturity (in years)	7 years 11 months 24 days	11 years 1 month 10 days	15 years 2 months 22 days