Mortgage Banking - Schedule of Mortgage Loans Sold and Serviced for Others (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	$ 6,687,057	$ 6,624,005
Federal National Mortgage Association [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	4,145,823	4,128,614
Government National Mortgage Association [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	2,452,399	2,421,456
Federal Home Loan Mortgage Corporation [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	64,686	47,071
Other [Member]
Mortgage Loans On Real Estate [Line Items]
Total mortgage loans sold and serviced for others	$ 24,149	$ 26,864