Fair Value Measurements - Summarizes Differences Between Fair Value and Principal Balance for Mortgage Loans Held for Sale Measure at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Summarizes differences between fair value and principal balance for mortgage loans held for sale measure at fair value
Mortgage loans held for sale measured at fair value	$ 392,448	$ 219,848
Aggregate Fair Value
Summarizes differences between fair value and principal balance for mortgage loans held for sale measure at fair value
Mortgage loans held for sale measured at fair value	392,448
Past due loans of 90 days or more	0
Nonaccrual loans	0
Aggregate Unpaid Principal Balance
Summarizes differences between fair value and principal balance for mortgage loans held for sale measure at fair value
Mortgage loans held for sale measured at fair value	379,727
Past due loans of 90 days or more	0
Nonaccrual loans	0
Difference
Summarizes differences between fair value and principal balance for mortgage loans held for sale measure at fair value
Mortgage loans held for sale measured at fair value	12,721
Past due loans of 90 days or more	0
Nonaccrual loans	$ 0