Derivative Activities - Other Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Derivative assets:
Derivative asset, before netting					$ 92,814	$ 85,046
Netting					(19,196)	(6,867)
Total derivative assets					73,618	78,179
Derivative liabilities:
Derivative liability, before netting					36,261	10,043
Netting					(23,568)	(4,247)
Net amounts of liabilities presented in the consolidated balance sheet					12,693	5,796
Interest Expense. | Repurchase agreement derivative
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Gains (losses) recognized on derivative financial instruments	$ (227)		$ (1,345)
Net gains on mortgage loans held for sale at fair value | Interest rate lock commitments and mortgage loans held for sale
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Gains (losses) recognized on derivative financial instruments	10,820	$ (26,981)	100,422	$ (27,191)
Net loan servicing fees | Mortgage servicing rights
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Gains (losses) recognized on derivative financial instruments	(52,971)	7,174	(180,853)	(17,018)
Margin Deposits
Derivative assets:
Derivative asset, before netting					(4,372)	2,620
Interest rate lock commitments
Derivative assets:
Total derivative assets					41,075	60,012
Interest rate lock commitments | Net gains on mortgage loans held for sale at fair value
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Gains (losses) recognized on derivative financial instruments	(18,526)	8,226	(21,109)	(5,008)
Forward contracts | Purchases
Derivative Instruments
Notional amount	7,115,621		4,920,883		7,115,621	4,920,883
Derivative assets:
Derivative asset, before netting					821	4,288
Derivative liabilities:
Derivative liability, before netting					29,569	1,272
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			4,920,883
Balance end of quarter	7,115,621		7,115,621
Forward contracts | Sales
Derivative Instruments
Notional amount	6,711,197		5,204,796		6,711,197	5,204,796
Derivative assets:
Derivative asset, before netting					16,892	2,101
Derivative liabilities:
Derivative liability, before netting					2,780	7,031
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			5,204,796
Balance end of quarter	6,711,197		6,711,197
MBS put options
Derivative Instruments
Notional amount	4,150,000		4,925,000		4,150,000	4,925,000
Derivative assets:
Derivative asset, before netting					4,413	3,481
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			4,925,000
Balance end of quarter	4,150,000		4,150,000
MBS call options
Derivative Instruments
Notional amount	1,250,000		1,250,000		1,250,000
Derivative assets:
Derivative asset, before netting					12
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance end of quarter	1,250,000		1,250,000
Put options on interest rate futures | Purchases
Derivative Instruments
Notional amount	2,225,000		2,125,000		2,225,000	2,125,000
Derivative assets:
Derivative asset, before netting					3,063	3,570
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			2,125,000
Balance end of quarter	2,225,000		2,225,000
Put options on interest rate futures | Sales
Derivative Instruments
Notional amount	300,000		300,000		300,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance end of quarter	300,000		300,000
Call options on interest rate futures | Purchases
Derivative Instruments
Notional amount	400,000		100,000		400,000	100,000
Derivative assets:
Derivative asset, before netting					63	938
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			100,000
Balance end of quarter	400,000		400,000
Treasury future | Purchases
Derivative Instruments
Notional amount	835,000		100,000		835,000	100,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			100,000
Balance end of quarter	835,000		835,000
Treasury future | Sales
Derivative Instruments
Notional amount	1,450,000		1,450,000		1,450,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance end of quarter	1,450,000		1,450,000
Interest rate swap futures | Purchases
Derivative Instruments
Notional amount			1,400,000			1,400,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			1,400,000
Interest rate swap futures | Sales
Derivative Instruments
Notional amount	625,000		625,000		625,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance end of quarter	625,000		625,000
Not designated as hedging instrument | Repurchase agreement derivatives
Derivative assets:
Derivative asset, before netting					26,475	10,656
Not designated as hedging instrument | Interest rate lock commitments
Derivative Instruments
Notional amount	3,388,437		3,654,955		3,388,437	3,654,955
Derivative assets:
Derivative asset, before netting					41,075	60,012
Derivative liabilities:
Derivative liability, before netting					3,912	1,740
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter			3,654,955
Balance end of quarter	3,388,437		3,388,437
Not designated as hedging instrument | Forward contracts | Purchases
Derivative Instruments
Notional amount	6,617,888	7,819,706	4,920,883	12,746,191	7,115,621	4,920,883
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	6,617,888	7,819,706	4,920,883	12,746,191
Additions	47,038,415	47,723,376	140,158,865	136,663,951
Dispositions/expirations	(46,540,682)	(48,242,564)	(137,964,127)	(142,109,624)
Balance end of quarter	7,115,621	7,300,518	7,115,621	7,300,518
Not designated as hedging instrument | Forward contracts | Sales
Derivative Instruments
Notional amount	7,107,202	7,641,979	5,204,796	16,577,942	6,711,197	5,204,796
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	7,107,202	7,641,979	5,204,796	16,577,942
Additions	58,521,199	61,239,459	174,562,881	169,173,906
Dispositions/expirations	(58,917,204)	(61,296,545)	(173,056,480)	(178,166,955)
Balance end of quarter	6,711,197	7,584,893	6,711,197	7,584,893
Not designated as hedging instrument | MBS put options
Derivative Instruments
Notional amount	2,675,000	6,075,000	4,925,000	1,175,000	4,150,000	4,925,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	2,675,000	6,075,000	4,925,000	1,175,000
Additions	8,375,000	6,825,000	17,250,000	19,675,000
Dispositions/expirations	(6,900,000)	(7,250,000)	(18,025,000)	(15,200,000)
Balance end of quarter	4,150,000	5,650,000	4,150,000	5,650,000
Not designated as hedging instrument | MBS call options
Derivative Instruments
Notional amount	1,250,000	650,000	1,250,000	1,600,000	1,250,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter				1,600,000
Additions	1,250,000	7,900,000	12,375,000	12,100,000
Dispositions/expirations		(7,250,000)	(11,125,000)	(13,050,000)
Balance end of quarter	1,250,000	650,000	1,250,000	650,000
Not designated as hedging instrument | Put options on interest rate futures | Purchases
Derivative Instruments
Notional amount	1,852,500	1,250,000	2,125,000	1,125,000	2,225,000	2,125,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	1,852,500	1,250,000	2,125,000	1,125,000
Additions	4,922,300	2,950,000	16,624,800	7,410,000
Dispositions/expirations	(4,549,800)	(3,175,000)	(16,524,800)	(7,510,000)
Balance end of quarter	2,225,000	1,025,000	2,225,000	1,025,000
Not designated as hedging instrument | Put options on interest rate futures | Sales
Derivative Instruments
Notional amount	300,000	200,000	300,000		300,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter		200,000
Additions	4,849,800	2,975,000	16,824,800	7,510,000
Dispositions/expirations	(4,549,800)	(3,175,000)	(16,524,800)	(7,510,000)
Balance end of quarter	300,000		300,000
Not designated as hedging instrument | Call options on interest rate futures | Purchases
Derivative Instruments
Notional amount	800,000	200,000	100,000	900,000	400,000	100,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	800,000	200,000	100,000	900,000
Additions	950,000	125,000	2,400,000	1,614,300
Dispositions/expirations	(1,350,000)	(200,000)	(2,100,000)	(2,389,300)
Balance end of quarter	400,000	125,000	400,000	125,000
Not designated as hedging instrument | Call options on interest rate futures | Sales
Derivative Instruments
Notional amount		125,000		125,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Additions	1,350,000	325,000	2,100,000	2,514,300
Dispositions/expirations	(1,350,000)	(200,000)	(2,100,000)	(2,389,300)
Balance end of quarter		125,000		125,000
Not designated as hedging instrument | Treasury future | Purchases
Derivative Instruments
Notional amount	835,000		100,000		835,000	100,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	835,000		100,000
Additions	2,557,100	46,500	7,453,300	212,600
Dispositions/expirations	(2,557,100)	(46,500)	(6,718,300)	(212,600)
Balance end of quarter	835,000		835,000
Not designated as hedging instrument | Treasury future | Sales
Derivative Instruments
Notional amount	1,450,000		1,450,000		1,450,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	1,450,000
Additions	2,557,100	46,500	8,829,600	212,600
Dispositions/expirations	(2,557,100)	(46,500)	(7,379,600)	(212,600)
Balance end of quarter	1,450,000		1,450,000
Not designated as hedging instrument | Interest rate swap futures | Purchases
Derivative Instruments
Notional amount	465,000	325,000	1,400,000	200,000		$ 1,400,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Balance at beginning of quarter	465,000	325,000	1,400,000	200,000
Additions	420,000	1,075,000	885,000	1,600,000
Dispositions/expirations	(885,000)		(2,285,000)	(400,000)
Balance end of quarter		$ 1,400,000		1,400,000
Not designated as hedging instrument | Interest rate swap futures | Sales
Derivative Instruments
Notional amount	625,000		625,000		$ 625,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Additions	885,000		2,285,000	400,000
Dispositions/expirations	(260,000)		(1,660,000)	$ (400,000)
Balance end of quarter	$ 625,000		$ 625,000