Fair Value - Fair Value Option Maturities, Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair value
Total fair value	$ 2,416,955	$ 3,099,103
Recurring basis
Fair value
Total fair value	2,416,955	3,099,103
Mortgage loans held for sale | Recurring basis
Fair value
Current through 89 days delinquent	2,148,919	2,430,517
Not in foreclosure	215,712	614,329
In foreclosure	52,324	54,257
Total fair value	2,416,955	3,099,103
Principal amount due upon maturity
Current through 89 days delinquent	2,078,047	2,326,772
Not in foreclosure	218,623	614,357
In foreclosure	56,101	57,248
Total principal amount due upon maturity	2,352,771	2,998,377
Difference
Current through 89 days delinquent	70,872	103,745
Not in foreclosure	(2,911)	(28)
In foreclosure	(3,777)	(2,991)
Total difference	$ 64,184	$ 100,726