Loans and Allowance for Credit Losses (Schedule of Credit Exposure for Loans Based on Original LTV and FICO Score) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss and Fee	$ 23,779,315	$ 23,154,988
Residential and Other Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss and Fee	5,940,900	5,661,119
1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	536,862	820,613
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	749,121	615,021
Financing Receivable, Originated Two Years before Latest Fiscal Year	434,232	835,512
Financing Receivable, before Allowance for Credit Loss and Fee	4,845,156	4,953,936
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,587,399	1,245,630
Financing Receivable, Originated Four Years before Latest Fiscal Year	836,015	644,937
Financing Receivable, Originated Three Years before Latest Fiscal Year	701,527	792,223
FICO, 760 or greater | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	411,055	470,057
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	515,046	340,716
Financing Receivable, Originated Two Years before Latest Fiscal Year	269,976	534,017
Financing Receivable, before Allowance for Credit Loss and Fee	3,418,425	3,073,107
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,084,645	763,807
Financing Receivable, Originated Four Years before Latest Fiscal Year	619,639	430,706
Financing Receivable, Originated Three Years before Latest Fiscal Year	518,064	533,804
FICO, 720 to 759 | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	94,190	242,806
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	141,462	185,939
Financing Receivable, Originated Two Years before Latest Fiscal Year	90,222	200,623
Financing Receivable, before Allowance for Credit Loss and Fee	870,636	1,256,450
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	282,188	307,195
Financing Receivable, Originated Four Years before Latest Fiscal Year	146,092	141,748
Financing Receivable, Originated Three Years before Latest Fiscal Year	116,482	178,139
FICO, 719 or less | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	31,617	107,750
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	92,613	88,366
Financing Receivable, Originated Two Years before Latest Fiscal Year	74,034	100,872
Financing Receivable, before Allowance for Credit Loss and Fee	556,095	624,379
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	220,566	174,628
Financing Receivable, Originated Four Years before Latest Fiscal Year	70,284	72,483
Financing Receivable, Originated Three Years before Latest Fiscal Year	66,981	80,280
Less than 61% [Member] | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	196,638	171,069
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	165,287	134,978
Financing Receivable, Originated Two Years before Latest Fiscal Year	91,845	183,807
Financing Receivable, before Allowance for Credit Loss and Fee	1,509,084	1,287,982
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	546,052	372,221
Financing Receivable, Originated Four Years before Latest Fiscal Year	314,274	197,039
Financing Receivable, Originated Three Years before Latest Fiscal Year	194,988	228,868
61% - 70% [Member] | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	150,811	195,572
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	177,825	128,766
Financing Receivable, Originated Two Years before Latest Fiscal Year	103,789	152,502
Financing Receivable, before Allowance for Credit Loss and Fee	1,163,785	1,136,034
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	386,857	316,031
Financing Receivable, Originated Four Years before Latest Fiscal Year	210,631	154,307
Financing Receivable, Originated Three Years before Latest Fiscal Year	133,872	188,856
71% - 80% [Member] | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	187,963	442,311
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	393,162	313,779
Financing Receivable, Originated Two Years before Latest Fiscal Year	210,356	404,743
Financing Receivable, before Allowance for Credit Loss and Fee	2,024,100	2,313,412
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	627,088	531,377
Financing Receivable, Originated Four Years before Latest Fiscal Year	291,439	283,202
Financing Receivable, Originated Three Years before Latest Fiscal Year	314,092	338,000
More than 81% [Member] | 1-4 single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,450	11,661
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	12,847	37,498
Financing Receivable, Originated Two Years before Latest Fiscal Year	28,242	94,460
Financing Receivable, before Allowance for Credit Loss and Fee	148,187	216,508
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	27,402	26,001
Financing Receivable, Originated Four Years before Latest Fiscal Year	19,671	10,389
Financing Receivable, Originated Three Years before Latest Fiscal Year	$ 58,575	$ 36,499