Mortgage Servicing Rights - Information of MSRs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Transfers and Servicing [Abstract]
Unpaid principal balance	$ 4,871,155	$ 4,635,712	$ 4,012,519
Weighted-average prepayment speed (CPR)	11.48%	7.95%	8.04%
Estimated impact of a 10% increase	$ (2,469)	$ (1,264)	$ (1,592)
Estimated impact of a 20% increase	$ (4,774)	$ (2,569)	$ (3,095)
Discount rate	9.69%	9.45%	9.69%
Estimated impact of a 100bp increase	$ (2,027)	$ (2,657)	$ (2,027)
Estimated impact of a 200bp increase	$ (3,908)	$ (5,103)	$ (3,896)
Weighted-average coupon interest rate	4.04%	4.04%	3.89%
Weighted-average servicing fee (basis points)	0.292%	0.2747%	0.2636%
Weighted-average remaining maturity (in years)	6 years 4 months 6 days	8 years 10 days	7 years 11 months 23 days