Fair Value - Level 3 Input Roll Forward, Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Mortgage servicing liabilities resulting from mortgage loan sales	$ 7,601	$ 17,229	$ 14,991
Excess servicing spread financing
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the year	236,534	288,669	412,425
Accrual of interest on excess servicing spread financing	15,138	16,951	22,601
Repayment	(46,750)	(54,980)	(69,992)
Changes in fair value included in income	8,500	(19,350)	(23,923)
Balance at the end of the year	216,110	236,534	288,669
Recurring basis
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	1,489,149	622,587	752,551
Reclassification of mortgage servicing rights previously accounted for under the amortization method	1,482,426
Balance after reclassification	2,971,575
Purchases		3,425,474	1,608,773
Purchases and issuances, net	3,455,544
Sales		(1,339,580)	(1,202,621)
Sales and repayments	(1,392,574)
Interest rate lock commitments issued, net			429,598
Mortgage servicing rights resulting from mortgage loan sales	591,757	24,471	17,319
Changes in fair value included in income arising from:
Changes in instrument specific credit risk		(1,794)	3,469
Changes in instrument specific credit risk	158
Other factors	(129,803)	28,868	(17,920)
Total changes in fair value included in income	(129,645)	27,074	(14,451)
Transfers from mortgage loans held for sale from Level 3 to Level 2	(2,128,551)	(851,935)	(410,735)
Transfers to real estate acquired in settlement of loans	(5,185)
Transfers from interest rate lock commitments to mortgage loans held for sale	(206,193)	(418,942)	(557,847)
Balance at the end of the quarter	3,156,728	1,489,149	622,587
Changes in fair value recognized during the period relating to assets still held at the end of the period	(80,309)	(28,850)	(101,460)
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the year	250,654	303,861	413,824
Issuances	2,688	5,244	6,603
Accrual of interest on excess servicing spread financing	15,138	16,951	22,601
Repayment	(46,750)	(54,980)	(69,992)
Settlement			(59,045)
Mortgage servicing liabilities resulting from mortgage loan sales	7,601	17,229	14,991
Mortgage servicing liability assumed			10,139
Changes in fair value included in income	(4,540)	(37,651)	(35,260)
Balance at the end of the year	224,791	250,654	303,861
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(4,540)	(37,651)	(28,050)
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 year	236,534	288,669	412,425
Issuances	2,688	5,244	6,603
Accrual of interest on excess servicing spread financing	15,138	16,951	22,601
Repayment	(46,750)	(54,980)	(69,992)
Settlement			(59,045)
Changes in fair value included in income	8,500	(19,350)	(23,923)
Balance at the end of the year	216,110	236,534	288,669
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	8,500	(19,350)	(16,713)
Recurring basis | Mortgage servicing liabilities
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the year	14,120	15,192	1,399
Mortgage servicing liabilities resulting from mortgage loan sales	7,601	17,229	14,991
Mortgage servicing liability assumed			10,139
Changes in fair value included in income	(13,040)	(18,301)	(11,337)
Balance at the end of the year	8,681	14,120	15,192
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(13,040)	(18,301)	(11,337)
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	782,211	47,271	48,531
Balance after reclassification	782,211
Purchases		2,928,249	1,608,627
Purchases and issuances, net	2,972,042
Sales		(1,339,580)	(1,202,621)
Sales and repayments	(1,360,667)
Changes in fair value included in income arising from:
Changes in instrument specific credit risk		(1,794)	3,469
Changes in instrument specific credit risk	158
Total changes in fair value included in income	158	(1,794)	3,469
Transfers from mortgage loans held for sale from Level 3 to Level 2	(2,128,551)	(851,935)	(410,735)
Transfers to real estate acquired in settlement of loans	(5,185)
Balance at the end of the quarter	260,008	782,211	47,271
Changes in fair value recognized during the period relating to assets still held at the end of the period	(263)	(556)	936
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	58,272	59,391	43,773
Balance after reclassification	58,272
Purchases		302,389
Purchases and issuances, net	195,974
Interest rate lock commitments issued, net			429,598
Changes in fair value included in income arising from:
Other factors	1,285	115,434	143,867
Total changes in fair value included in income	1,285	115,434	143,867
Transfers from interest rate lock commitments to mortgage loans held for sale	(206,193)	(418,942)	(557,847)
Balance at the end of the quarter	49,338	58,272	59,391
Changes in fair value recognized during the period relating to assets still held at the end of the period	49,338	58,272	59,391
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	10,656
Balance after reclassification	10,656
Purchases		10,986
Purchases and issuances, net	49,725
Sales and repayments	(31,907)
Changes in fair value included in income arising from:
Other factors	(1,704)	(330)
Total changes in fair value included in income	(1,704)	(330)
Balance at the end of the quarter	26,770	10,656
Changes in fair value recognized during the period relating to assets still held at the end of the period		(330)
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	638,010	515,925	660,247
Reclassification of mortgage servicing rights previously accounted for under the amortization method	1,482,426
Balance after reclassification	2,120,436
Purchases		183,850	146
Purchases and issuances, net	237,803
Mortgage servicing rights resulting from mortgage loan sales	591,757	24,471	17,319
Changes in fair value included in income arising from:
Other factors	(129,384)	(86,236)	(161,787)
Total changes in fair value included in income	(129,384)	(86,236)	(161,787)
Balance at the end of the quarter	2,820,612	638,010	515,925
Changes in fair value recognized during the period relating to assets still held at the end of the period	$ (129,384)	$ (86,236)	$ (161,787)