Mortgage Servicing Rights - Information of MSRs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Transfers and Servicing [Abstract]
Unpaid principal balance	$ 7,322,671	$ 4,871,155	$ 4,635,712
Weighted-average prepayment speed (CPR)	15.05%	11.48%	7.95%
Estimated impact of a 10% increase	$ (4,001)	$ (2,469)	$ (1,264)
Estimated impact of a 20% increase	$ (7,674)	$ (4,774)	$ (2,569)
Discount rate	9.86%	9.69%	9.45%
Estimated impact of a 100bp increase	$ (2,144)	$ (2,027)	$ (2,657)
Estimated impact of a 200bp increase	$ (4,144)	$ (3,908)	$ (5,103)
Weighted-average coupon interest rate	3.58%	4.04%	4.04%
Weighted-average servicing fee (basis points)	0.2994%	0.292%	0.2747%
Weighted-average remaining maturity (in years)	5 years 1 month 20 days	6 years 4 months 6 days	8 years 10 days