Fair Value - Changes in Fair Value, Fair Value Option, Recurring Basis (Details) - Recurring basis - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Liabilities.
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	$ 2,019	$ 1,116	$ 13,039	$ 873
Liabilities. | Net loan servicing fees
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	2,019	1,116	13,039	873
Excess servicing spread financing
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	3,864	(1,109)	11,519	(9,026)
Excess servicing spread financing | Net loan servicing fees
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	3,864	(1,109)	11,519	(9,026)
Mortgage servicing liabilities
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	(1,845)	2,225	1,520	9,899
Mortgage servicing liabilities | Net loan servicing fees
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	(1,845)	2,225	1,520	9,899
Assets
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	(147,546)	55,005	(499,557)	141,736
Assets | Net gains on loans held for sale at fair value
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	263,339	67,709	538,086	118,452
Assets | Net loan servicing fees
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	(410,885)	(12,704)	(1,037,643)	23,284
Loans held for sale
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	263,339	67,709	538,086	118,452
Loans held for sale | Net gains on loans held for sale at fair value
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	263,339	67,709	538,086	118,452
Mortgage servicing rights at fair value
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	(410,885)	(12,704)	(1,037,643)	23,284
Mortgage servicing rights at fair value | Net loan servicing fees
Net gains (losses) from changes in estimated fair values included in earnings for financial statement items carried at estimated fair value
Total gains (losses) from changes in estimated fair values included in earnings	$ (410,885)	$ (12,704)	$ (1,037,643)	$ 23,284