Fair Value - Level 3 Input Roll Forward, Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2018
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Mortgage servicing liabilities resulting from mortgage loan sales	$ 794	$ 2,037
Excess servicing spread financing
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	216,110	236,534
Accrual of interest on excess servicing spread financing	3,066	3,934
Repayment	(10,552)	(12,291)
Changes in fair value included in income	(4,051)	6,921
Balance at the end of the quarter	205,081	236,002
Recurring basis
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	3,156,728	1,489,149
Reclassification of mortgage servicing rights previously accounted for under the amortization method			$ 1,482,426
Balance after reclassification			2,971,575
Purchases	1,078,872	751,224
Sales and repayments	(187,738)	(604,101)
Mortgage servicing rights resulting from mortgage loan sales	115,751	143,910
Changes in fair value included in income arising from:
Changes in instrument specific credit risk	(6,091)	(8,755)
Other factors	(199,624)	17,198
Total changes in fair value included in income	(205,715)	8,443
Transfers from mortgage loans held for sale from Level 3 to Level 2	(405,163)	(356,232)
Transfers to real estate acquired in settlement of loans	(1,181)
Transfers from interest rate lock commitments to mortgage loans held for sale	(100,234)	(28,061)
Balance at the end of the quarter	3,451,320	2,886,758
Changes in fair value recognized during the period relating to assets still held at the end of the period	(196,520)	105,758
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	224,791	250,654
Issuances	508	904
Accrual of interest on excess servicing spread financing	3,066	3,934
Repayment	(10,552)	(12,291)
Mortgage servicing liabilities resulting from mortgage loan sales	794	2,037
Changes in fair value included in income	(5,682)	2,827
Balance at the end of the quarter	212,925	248,065
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(5,682)	2,827
Recurring basis | Excess servicing spread financing
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	216,110	236,534
Issuances	508	904
Accrual of interest on excess servicing spread financing	3,066	3,934
Repayment	(10,552)	(12,291)
Changes in fair value included in income	(4,051)	6,921
Balance at the end of the quarter	205,081	236,002
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(4,051)	6,921
Recurring basis | Mortgage servicing liabilities
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	8,681	14,120
Mortgage servicing liabilities resulting from mortgage loan sales	794	2,037
Changes in fair value included in income	(1,631)	(4,094)
Balance at the end of the quarter	7,844	12,063
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(1,631)	(4,094)
Recurring basis | Mortgage loans held for sale
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	260,008	782,211
Balance after reclassification			782,211
Purchases	784,262	647,269
Sales and repayments	(176,302)	(604,094)
Changes in fair value included in income arising from:
Changes in instrument specific credit risk	(6,091)	(8,755)
Total changes in fair value included in income	(6,091)	(8,755)
Transfers from mortgage loans held for sale from Level 3 to Level 2	(405,163)	(356,232)
Transfers to real estate acquired in settlement of loans	(1,181)
Balance at the end of the quarter	455,533	460,399
Changes in fair value recognized during the period relating to assets still held at the end of the period	(3,540)	(7,598)
Recurring basis | Interest rate lock commitments
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	49,338	58,272
Balance after reclassification			58,272
Purchases	56,983	65,598
Changes in fair value included in income arising from:
Other factors	59,978	(44,913)
Total changes in fair value included in income	59,978	(44,913)
Transfers from interest rate lock commitments to mortgage loans held for sale	(100,234)	(28,061)
Balance at the end of the quarter	66,065	50,896
Changes in fair value recognized during the period relating to assets still held at the end of the period	66,065	50,896
Recurring basis | Repurchase agreement derivatives
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	26,770	10,656
Balance after reclassification			10,656
Purchases	9,855	10,751
Sales and repayments	(11,436)	(7)
Changes in fair value included in income arising from:
Other factors	(557)	(426)
Total changes in fair value included in income	(557)	(426)
Balance at the end of the quarter	24,632	20,974
Changes in fair value recognized during the period relating to assets still held at the end of the period		(77)
Recurring basis | Mortgage servicing rights
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	2,820,612	638,010
Reclassification of mortgage servicing rights previously accounted for under the amortization method			1,482,426
Balance after reclassification			$ 2,120,436
Purchases	227,772	27,606
Mortgage servicing rights resulting from mortgage loan sales	115,751	143,910
Changes in fair value included in income arising from:
Other factors	(259,045)	62,537
Total changes in fair value included in income	(259,045)	62,537
Balance at the end of the quarter	2,905,090	2,354,489
Changes in fair value recognized during the period relating to assets still held at the end of the period	$ (259,045)	$ 62,537