Allowance for Credit Losses and Allowance for Unfunded Commitments and Letters of Credit (Analysis of Credit Quality of the Loan Portfolio) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 998,511	$ 2,223,383
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,934,401	1,379,336
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,318,312	985,423
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	919,885	875,545
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	826,670	812,034
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,042,270	1,413,553
Financing Receivable, Revolving	1,617,657	1,687,345
Financing Receivable, Revolving Converted to Term Loans	18,612	51,041
Loans and Leases Receivable, Net of Deferred Income	9,676,318	9,427,660
Financing Receivable, Allowance for Credit Loss	148,294	149,140	$ 122,074	$ 83,968
Loans, net	9,528,024	9,278,520
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	205,152	680,708
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	675,249	709,562
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	703,398	513,737
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	495,541	547,996
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	527,418	498,904
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,420,546	1,038,233
Financing Receivable, Revolving	51,830	55,443
Financing Receivable, Revolving Converted to Term Loans	2,781	17,730
Loans and Leases Receivable, Net of Deferred Income	4,081,915	4,062,313
Financing Receivable, Allowance for Credit Loss	57,050	68,934	37,122	20,340
Commercial Real Estate [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	205,152	674,444
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	668,655	645,328
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	603,542	478,881
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	459,888	502,112
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	491,550	408,972
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,229,742	946,980
Financing Receivable, Revolving	49,274	52,049
Financing Receivable, Revolving Converted to Term Loans	2,781	11,332
Loans and Leases Receivable, Net of Deferred Income	3,710,584	3,720,098
Commercial Real Estate [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	3,348
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,127	39,374
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	65,107	21,285
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	19,094	30,232
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	4,420	46,197
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	99,370	50,115
Financing Receivable, Revolving	5	5
Financing Receivable, Revolving Converted to Term Loans	0	2,139
Loans and Leases Receivable, Net of Deferred Income	191,123	192,695
Commercial Real Estate [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	2,916
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,467	24,860
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	34,749	13,571
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	16,559	15,652
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	31,448	43,735
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	91,434	41,138
Financing Receivable, Revolving	2,551	3,389
Financing Receivable, Revolving Converted to Term Loans	0	4,259
Loans and Leases Receivable, Net of Deferred Income	180,208	149,520
Commercial Business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	586,311	1,094,027
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	836,347	400,172
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	382,654	343,892
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	316,401	229,497
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	207,952	231,713
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	411,159	229,070
Financing Receivable, Revolving	1,038,686	1,055,285
Financing Receivable, Revolving Converted to Term Loans	13,303	14,312
Loans and Leases Receivable, Net of Deferred Income	3,792,813	3,597,968
Financing Receivable, Allowance for Credit Loss	58,405	45,250	45,570	30,292
Commercial Business [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	586,311	1,087,400
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	829,165	366,435
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	347,668	324,360
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	273,408	199,010
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	178,663	218,313
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	376,297	214,677
Financing Receivable, Revolving	945,271	1,000,725
Financing Receivable, Revolving Converted to Term Loans	12,322	11,540
Loans and Leases Receivable, Net of Deferred Income	3,549,105	3,422,460
Commercial Business [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	3,002
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	588	26,361
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	8,346	8,471
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	6,237	24,582
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	2,063	7,004
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,131	10,650
Financing Receivable, Revolving	49,369	22,426
Financing Receivable, Revolving Converted to Term Loans	143	0
Loans and Leases Receivable, Net of Deferred Income	67,877	102,496
Commercial Business [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	3,625
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	6,594	7,376
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	26,640	11,061
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	36,756	5,905
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	27,226	6,396
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	33,731	3,743
Financing Receivable, Revolving	44,046	32,134
Financing Receivable, Revolving Converted to Term Loans	838	2,772
Loans and Leases Receivable, Net of Deferred Income	175,831	73,012
Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	57,282	147,356
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	130,931	103,182
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	97,275	50,587
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	42,786	62,657
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	60,778	59,177
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	112,534	62,898
Financing Receivable, Revolving	248,920	283,000
Financing Receivable, Revolving Converted to Term Loans	1,294	10,770
Loans and Leases Receivable, Net of Deferred Income	751,800	779,627
Financing Receivable, Allowance for Credit Loss	9,487	9,052	11,085	15,835
Agriculture [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	57,282	142,163
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	121,511	90,612
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	85,485	44,434
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	39,930	58,366
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	56,638	58,893
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	106,969	59,396
Financing Receivable, Revolving	209,154	244,135
Financing Receivable, Revolving Converted to Term Loans	550	9,299
Loans and Leases Receivable, Net of Deferred Income	677,519	707,298
Agriculture [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,398	90
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,366	285
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	163	33
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,371	0
Financing Receivable, Revolving	7,962	85
Financing Receivable, Revolving Converted to Term Loans	0	13
Loans and Leases Receivable, Net of Deferred Income	15,260	506
Agriculture [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	5,193
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	6,022	12,480
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	10,424	5,868
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,693	4,258
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	4,140	284
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	3,194	3,502
Financing Receivable, Revolving	31,804	38,780
Financing Receivable, Revolving Converted to Term Loans	744	1,458
Loans and Leases Receivable, Net of Deferred Income	59,021	71,823
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	41,447	134,693
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	130,122	84,706
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	62,269	10,066
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	7,909	3,498
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3,471	763
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	5,634	1,861
Financing Receivable, Revolving	31,682	29,323
Financing Receivable, Revolving Converted to Term Loans	0	3,753
Loans and Leases Receivable, Net of Deferred Income	282,534	268,663
Financing Receivable, Allowance for Credit Loss	6,551	7,636	8,845	8,571
Construction [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	41,447	134,693
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	130,122	66,974
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	44,121	10,066
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	7,909	3,498
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3,471	763
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	5,579	1,805
Financing Receivable, Revolving	31,682	29,323
Financing Receivable, Revolving Converted to Term Loans	0	3,753
Loans and Leases Receivable, Net of Deferred Income	264,331	250,875
Construction [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Revolving	0
Financing Receivable, Revolving Converted to Term Loans	0
Loans and Leases Receivable, Net of Deferred Income	0
Construction [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0	17,732
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	18,148	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	55	56
Financing Receivable, Revolving	0	0
Financing Receivable, Revolving Converted to Term Loans	0	0
Loans and Leases Receivable, Net of Deferred Income	18,203	17,788
One-to-Four Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	106,212	161,021
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	158,121	78,605
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	69,870	63,255
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	53,998	30,903
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	26,177	21,233
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	91,183	80,261
Financing Receivable, Revolving	229,226	244,330
Financing Receivable, Revolving Converted to Term Loans	527	3,962
Loans and Leases Receivable, Net of Deferred Income	735,314	683,570
Financing Receivable, Allowance for Credit Loss	15,638	16,875	17,659	7,435
One-to-Four Family Residential [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	106,212	161,021
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	157,286	77,756
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	68,489	62,696
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	53,753	29,737
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	25,686	20,889
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	88,323	78,098
Financing Receivable, Revolving	228,917	243,325
Financing Receivable, Revolving Converted to Term Loans	308	3,655
Loans and Leases Receivable, Net of Deferred Income	728,974	677,177
One-to-Four Family Residential [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0	332
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	125	195
Financing Receivable, Revolving	0	0
Financing Receivable, Revolving Converted to Term Loans	0	0
Loans and Leases Receivable, Net of Deferred Income	125	527
One-to-Four Family Residential [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	835	849
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,381	227
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	245	1,166
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	491	344
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,735	1,968
Financing Receivable, Revolving	309	1,005
Financing Receivable, Revolving Converted to Term Loans	219	307
Loans and Leases Receivable, Net of Deferred Income	6,215	5,866
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,107	5,578
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,631	3,109
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,846	3,886
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	3,250	994
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	874	244
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,214	1,230
Financing Receivable, Revolving	17,313	19,964
Financing Receivable, Revolving Converted to Term Loans	707	514
Loans and Leases Receivable, Net of Deferred Income	31,942	35,519
Financing Receivable, Allowance for Credit Loss	1,163	1,393	$ 1,644	$ 883
Consumer Loan [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,107	5,548
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,595	3,109
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,807	3,886
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	3,250	989
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	871	244
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,211	1,060
Financing Receivable, Revolving	17,277	19,911
Financing Receivable, Revolving Converted to Term Loans	610	474
Loans and Leases Receivable, Net of Deferred Income	31,728	35,221
Consumer Loan [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	30
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	36	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	39	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0	5
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	3	170
Financing Receivable, Revolving	36	53
Financing Receivable, Revolving Converted to Term Loans	97	40
Loans and Leases Receivable, Net of Deferred Income	$ 214	$ 298