Derivative Activities - Other Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Derivative assets:
Derivative asset, before netting				$ 123,316	$ 85,046
Netting				(26,969)	(6,867)
Total derivative assets				96,347	78,179
Derivative liabilities:
Derivative liability, before netting				28,146	10,043
Netting				(25,082)	(4,247)
Net amounts of liabilities presented in the consolidated balance sheet				3,064	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	$ (1,704)	$ (330)
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	81,522	(21,255)	$ 20,619
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	(121,045)	(37,855)	26,405
Margin Deposits
Derivative assets:
Margin deposit assets				1,887	2,620
Interest rate lock commitments
Derivative assets:
Total derivative assets				50,507	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	(8,934)	(1,120)	15,618
Not designated as hedging instrument | Repurchase agreement derivatives
Derivative assets:
Derivative asset, before netting				26,770	10,656
Not designated as hedging instrument | Interest rate lock commitments
Derivative Instruments
Notional amount	3,654,955	3,654,955		2,805,400	3,654,955
Derivative assets:
Derivative asset, before netting				50,507	60,012
Derivative liabilities:
Derivative liability, before netting				1,169	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	2,805,400	3,654,955
Not designated as hedging instrument | Forward contracts | Purchases
Derivative Instruments
Notional amount	4,920,883	12,746,191	5,254,293	6,657,026	4,920,883
Derivative assets:
Derivative asset, before netting				35,916	4,288
Derivative liabilities:
Derivative liability, before netting				215	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	12,746,191	5,254,293
Additions	184,780,152	181,761,564	210,412,697
Dispositions/expirations	(183,044,009)	(189,586,872)	(202,920,799)
Balance end of quarter	6,657,026	4,920,883	12,746,191
Not designated as hedging instrument | Forward contracts | Sales
Derivative Instruments
Notional amount	5,204,796	16,577,942	6,230,811	6,890,046	5,204,796
Derivative assets:
Derivative asset, before netting				437	2,101
Derivative liabilities:
Derivative liability, before netting				26,762	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	16,577,942	6,230,811
Additions	230,735,936	226,000,107	262,202,884
Dispositions/expirations	(229,050,686)	(237,373,253)	(251,855,753)
Balance end of quarter	6,890,046	5,204,796	16,577,942
Not designated as hedging instrument | MBS put options
Derivative Instruments
Notional amount	4,925,000	1,175,000	1,275,000	4,635,000	4,925,000
Derivative assets:
Derivative asset, before netting				720	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	1,175,000	1,275,000
Additions	31,085,000	25,050,000	19,225,000
Dispositions/expirations	(31,375,000)	(21,300,000)	(19,325,000)
Balance end of quarter	4,635,000	4,925,000	1,175,000
Not designated as hedging instrument | MBS call options
Derivative Instruments
Notional amount	1,450,000	1,600,000	1,600,000	1,450,000
Derivative assets:
Derivative asset, before netting				2,135
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	14,325,000	17,700,000	1,600,000
Dispositions/expirations	(12,875,000)	(19,300,000)
Balance end of quarter	1,450,000		1,600,000
Not designated as hedging instrument | Put options on interest rate futures | Purchases
Derivative Instruments
Notional amount	2,125,000	1,125,000	1,650,000	3,085,000	2,125,000
Derivative assets:
Derivative asset, before netting				866	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	1,125,000	1,650,000
Additions	20,559,800	11,360,000	15,331,000
Dispositions/expirations	(19,599,800)	(10,360,000)	(15,856,000)
Balance end of quarter	3,085,000	2,125,000	1,125,000
Not designated as hedging instrument | Put options on interest rate futures | Sales
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Additions	20,474,800	10,010,000	9,436,000
Dispositions/expirations	(20,474,800)	(10,010,000)	(9,436,000)
Not designated as hedging instrument | Call options on interest rate futures | Purchases
Derivative Instruments
Notional amount	100,000	900,000	600,000	1,512,500	100,000
Derivative assets:
Derivative asset, before netting				5,965	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	900,000	600,000
Additions	4,387,500	1,939,300	5,687,500
Dispositions/expirations	(2,975,000)	(2,739,300)	(5,387,500)
Balance end of quarter	1,512,500	100,000	900,000
Not designated as hedging instrument | Call options on interest rate futures | Sales
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Additions	2,100,000	2,739,300	550,000
Dispositions/expirations	(2,100,000)	(2,739,300)	(550,000)
Not designated as hedging instrument | Treasury future | Purchases
Derivative Instruments
Notional amount	100,000	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
Additions	9,837,500	544,900	585,800
Dispositions/expirations	(9,102,500)	(444,900)	(585,800)
Balance end of quarter	835,000	100,000
Not designated as hedging instrument | Treasury future | Sales
Derivative Instruments
Notional amount	1,450,000			1,450,000
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Additions	11,213,800	444,900	585,800
Dispositions/expirations	(9,763,800)	(444,900)	(585,800)
Balance end of quarter	1,450,000
Not designated as hedging instrument | Interest rate swap futures | Purchases
Derivative Instruments
Notional amount	1,400,000	200,000	200,000	$ 625,000	$ 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	200,000
Additions	1,510,000	2,100,000	400,000
Dispositions/expirations	(2,285,000)	(900,000)	(200,000)
Balance end of quarter	625,000	1,400,000	200,000
Not designated as hedging instrument | Interest rate swap futures | Sales
Activity for derivative contracts used to hedge the IRLCs and inventory of mortgage loans at notional value
Additions	2,285,000	900,000	200,000
Dispositions/expirations	$ (2,285,000)	$ (900,000)	$ (200,000)