Fair Value - Level 3 Input Roll Forward, Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 02, 2018
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Mortgage servicing liabilities resulting from mortgage loan sales			$ 5,548	$ 11,940
Excess servicing spread financing
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	$ 229,470	$ 261,796	236,534	288,669
Accrual of interest on excess servicing spread financing	3,740	3,998	11,584	13,011
Repayment	(11,543)	(13,410)	(35,852)	(42,320)
Changes in fair value included in income	1,109	(4,828)	9,026	(14,757)
Balance at the end of the quarter	223,275	248,763	223,275	248,763
Recurring basis
Roll forward of assets measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	2,901,793	1,104,683	1,489,149	622,587
Reclassification of mortgage servicing rights previously accounted for under the amortization method					$ 1,482,426
Balance after reclassification					2,971,575
Purchases	1,226,797		2,868,436	2,226,425
Purchases and issuances, net		583,854
Sales and repayments	(243,903)	(306,458)	(1,141,908)	(845,318)
Mortgage servicing rights resulting from mortgage loan sales	149,000	5,773	448,604	19,702
Changes in fair value included in income arising from:
Changes in instrument specific credit risk	84	(1,130)	(4,944)	(6,104)
Other factors	(2,235)	13,422	(6,688)	35,952
Total changes in fair value included in income	(2,151)	12,292	(11,632)	29,848
Transfers from mortgage loans held for sale from Level 3 to Level 2	(744,324)	(195,802)	(1,765,854)	(635,118)
Transfers to real estate acquired in settlement of loans	(1,364)		(4,185)
Transfers from interest rate lock commitments to mortgage loans held for sale	(70,943)	(117,265)	(150,131)	(331,049)
Balance at the end of the quarter	3,214,905	1,087,077	3,214,905	1,087,077
Changes in fair value recognized during the period relating to assets still held at the end of the period	19,648	23,262	55,535	(12,822)
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Balance at the beginning of the quarter	239,723	280,091	250,654	303,861
Issuances			1,983	4,160
Accrual of interest on excess servicing spread financing	3,740	3,998	11,584	13,011
Repayment		(13,410)	(35,852)	(42,320)
Settlement	(11,543)
Mortgage servicing liabilities resulting from mortgage loan sales	1,741	4,071	5,548	11,940
Changes in fair value included in income	(1,116)	(11,118)	(873)	(25,813)
Balance at the end of the quarter	233,044	264,839	233,044	264,839
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(1,116)	(11,118)	(873)	(25,813)
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	229,470	261,796	236,534	288,669
Issuances			1,983	4,160
Accrual of interest on excess servicing spread financing	3,740	3,998	11,584	13,011
Repayment		(13,410)	(35,852)	(42,320)
Settlement	(11,543)
Changes in fair value included in income	1,109	(4,828)	9,026	(14,757)
Balance at the end of the quarter	223,275	248,763	223,275	248,763
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	1,109	(4,828)	9,026	(14,757)
Recurring basis | Excess Servicing Spread Financing Pursuant to Recapture Agreement
Roll forward of liabilities measured using Level 3 inputs on a recurring basis
Issuances	499	1,207
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	10,253	18,295	14,120	15,192
Mortgage servicing liabilities resulting from mortgage loan sales	1,741	4,071	5,548	11,940
Changes in fair value included in income	(2,225)	(6,290)	(9,899)	(11,056)
Balance at the end of the quarter	9,769	16,076	9,769	16,076
Changes in fair value recognized during the period relating to liability still outstanding at the end of the period	(2,225)	(6,290)	(9,899)	(11,056)
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	334,166	380,084	782,211	47,271
Balance after reclassification					782,211
Purchases	1,008,662		2,480,523	1,815,509
Purchases and issuances, net		499,546
Sales and repayments	(231,921)	(306,458)	(1,122,448)	(845,318)
Changes in fair value included in income arising from:
Changes in instrument specific credit risk	84	(1,130)	(4,944)	(6,104)
Total changes in fair value included in income	84	(1,130)	(4,944)	(6,104)
Transfers from mortgage loans held for sale from Level 3 to Level 2	(744,324)	(195,802)	(1,765,854)	(635,118)
Transfers to real estate acquired in settlement of loans	(1,364)		(4,185)
Balance at the end of the quarter	365,303	376,240	365,303	376,240
Changes in fair value recognized during the period relating to assets still held at the end of the period	(4,811)	(2,851)	(4,912)	(3,733)
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	55,689	46,158	58,272	59,391
Balance after reclassification					58,272
Purchases	41,721		157,649	226,617
Purchases and issuances, net		83,798
Changes in fair value included in income arising from:
Other factors	10,696	41,693	(28,627)	99,425
Total changes in fair value included in income	10,696	41,693	(28,627)	99,425
Transfers from interest rate lock commitments to mortgage loans held for sale	(70,943)	(117,265)	(150,131)	(331,049)
Balance at the end of the quarter	37,163	54,384	37,163	54,384
Changes in fair value recognized during the period relating to assets still held at the end of the period	37,163	54,384	37,163	54,384
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	25,781		10,656
Balance after reclassification					10,656
Purchases	12,903		36,624	469
Purchases and issuances, net		469
Sales and repayments	(11,982)		(19,460)
Changes in fair value included in income arising from:
Other factors	(227)		(1,345)
Total changes in fair value included in income	(227)		(1,345)
Balance at the end of the quarter	26,475	469	26,475	469
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	2,486,157	678,441	638,010	515,925
Reclassification of mortgage servicing rights previously accounted for under the amortization method					1,482,426
Balance after reclassification					$ 2,120,436
Purchases	163,511		193,640	183,830
Purchases and issuances, net		41
Mortgage servicing rights resulting from mortgage loan sales	149,000	5,773	448,604	19,702
Changes in fair value included in income arising from:
Other factors	(12,704)	(28,271)	23,284	(63,473)
Total changes in fair value included in income	(12,704)	(28,271)	23,284	(63,473)
Balance at the end of the quarter	2,785,964	655,984	2,785,964	655,984
Changes in fair value recognized during the period relating to assets still held at the end of the period	$ (12,704)	$ (28,271)	$ 23,284	$ (63,473)