Fair Value - Changes in Fair Value, Fair Value Option, Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 26,785	$ 4,540	$ 37,651
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	26,785	4,540	37,651
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	9,256	(8,500)	19,350
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	9,256	(8,500)	19,350
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	17,529	13,040	18,301
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	17,529	13,040	18,301
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	(194,248)	59,227	339,856
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	811,895	188,611	426,092
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	(1,006,143)	(129,384)	(86,236)
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	811,895	188,611	426,092
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	811,895	188,611	426,092
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	(1,006,143)	(129,384)	(86,236)
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	$ (1,006,143)	$ (129,384)	$ (86,236)