Mortgage Banking - Schedule of Mortgage Loans Sold and Serviced for Others (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	$ 6,859,593	$ 6,834,874
Federal National Mortgage Association [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	4,205,947	4,204,336
Government National Mortgage Association [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	2,554,666	2,537,238
Federal Home Loan Mortgage Corporation [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	77,742	71,343
Other [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	$ 21,238	$ 21,957