Mortgage Servicing Rights - (Details 1) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Data and key economic assumptions related to mortgage servicing rights
Unpaid principal balance	$ 3,045,228	$ 2,763,344
Weighted-average prepayment speed (CPR) (as percent)	7.28%	7.34%
Estimated impact of a 10% increase	$ (1,147)	$ (1,034)
Estimated impact of a 20% increase	$ (2,234)	$ (2,010)
Discount rate (as percent)	9.65%	9.64%
Estimated impact of a 10% increase	$ (1,620)	$ (1,368)
Estimated impact of a 20% increase	$ (3,110)	$ (2,629)
Weighted-average coupon interest rate (as percent)	3.82%	3.83%
Weighted-average servicing fee (basis points) (as percent)	0.2589%	0.2587%
Weighted-average remaining maturity (in years)	12 years 5 months 26 days	11 years 1 month 11 days