Fair Value - Fair Value Option Maturities, Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair value
Total fair value	$ 4,522,971	$ 2,521,647
Recurring basis
Fair value
Total fair value	4,522,971	2,521,647
Loans held for sale | Recurring basis
Fair value
Current through 89 days delinquent	4,478,965	2,324,203
Not in foreclosure	20,972	143,631
In foreclosure	23,034	53,813
Total fair value	4,522,971	2,521,647
Principal amount due upon maturity
Current through 89 days delinquent	4,275,981	2,220,371
Not in foreclosure	22,145	144,011
In foreclosure	25,126	56,254
Total principal amount due upon maturity	4,323,252	2,420,636
Difference
Current through 89 days delinquent	202,984	103,832
Not in foreclosure	(1,173)	(380)
In foreclosure	(2,092)	(2,441)
Total difference	$ 199,719	$ 101,011