Fair Value Measurements - Summarizes Differences Between Fair Value and Principal Balance for Mortgage Loans Held for Sale Measure at Fair Value (Details) $ in Thousands	Jun. 30, 2018 USD ($)
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	$ 245,046
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	237,373
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	7,673
Past due loans of 90 days or more	0
Nonaccrual loans	$ 0