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	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 1,621,922		$ 2,223,383
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,615,362		1,379,336
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,239,041		985,423
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	854,436		875,545
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	785,447		812,034
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,855,933		1,413,553
Financing Receivable, Revolving	1,693,637		1,687,345
Financing Receivable, Revolving Converted to Term Loans	27,338		51,041
Loans and Leases Receivable, Net of Deferred Income	9,693,116		9,427,660
Financing Receivable, Allowance for Credit Loss	142,988	$ 148,294	149,140	$ 151,546	$ 122,074	$ 83,968
Loans, net	9,550,128		9,278,520
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	392,208		680,708
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	662,336		709,562
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	686,516		513,737
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	475,990		547,996
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	508,073		498,904
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,312,274		1,038,233
Financing Receivable, Revolving	58,704		55,443
Financing Receivable, Revolving Converted to Term Loans	4,970		17,730
Loans and Leases Receivable, Net of Deferred Income	4,101,071		4,062,313
Financing Receivable, Allowance for Credit Loss	53,250	57,050	68,934	50,233	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	389,826		674,444
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	648,251		645,328
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	584,280		478,881
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	443,700		502,112
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	452,989		408,972
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,163,730		946,980
Financing Receivable, Revolving	57,550		52,049
Financing Receivable, Revolving Converted to Term Loans	2,775		11,332
Loans and Leases Receivable, Net of Deferred Income	3,743,101		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	1,875		3,348
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	10,168		39,374
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	58,636		21,285
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	21,408		30,232
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	26,722		46,197
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	60,889		50,115
Financing Receivable, Revolving	0		5
Financing Receivable, Revolving Converted to Term Loans	2,195		2,139
Loans and Leases Receivable, Net of Deferred Income	181,893		192,695
Commercial Real Estate [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	507		2,916
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,917		24,860
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	43,600		13,571
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	10,882		15,652
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	28,362		43,735
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	87,655		41,138
Financing Receivable, Revolving	1,154		3,389
Financing Receivable, Revolving Converted to Term Loans	0		4,259
Loans and Leases Receivable, Net of Deferred Income	176,077		149,520
Commercial Business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	881,837		1,094,027
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	593,050		400,172
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	358,688		343,892
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	281,579		229,497
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	190,264		231,713
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	349,329		229,070
Financing Receivable, Revolving	1,065,097		1,055,285
Financing Receivable, Revolving Converted to Term Loans	18,444		14,312
Loans and Leases Receivable, Net of Deferred Income	3,738,288		3,597,968
Financing Receivable, Allowance for Credit Loss	57,554	58,405	45,250	53,186	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	881,501		1,087,400
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	585,999		366,435
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	325,418		324,360
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	245,432		199,010
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	163,134		218,313
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	316,525		214,677
Financing Receivable, Revolving	980,429		1,000,725
Financing Receivable, Revolving Converted to Term Loans	16,876		11,540
Loans and Leases Receivable, Net of Deferred Income	3,515,314		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	1,243		26,361
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	8,311		8,471
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	6,293		24,582
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	4,955		7,004
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	990		10,650
Financing Receivable, Revolving	43,386		22,426
Financing Receivable, Revolving Converted to Term Loans	251		0
Loans and Leases Receivable, Net of Deferred Income	65,429		102,496
Commercial Business [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	336		3,625
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,808		7,376
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	24,959		11,061
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	29,854		5,905
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	22,175		6,396
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	31,814		3,743
Financing Receivable, Revolving	41,282		32,134
Financing Receivable, Revolving Converted to Term Loans	1,317		2,772
Loans and Leases Receivable, Net of Deferred Income	157,545		73,012
Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	98,017		147,356
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	106,789		103,182
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	93,316		50,587
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	39,034		62,657
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	58,665		59,177
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	105,005		62,898
Financing Receivable, Revolving	294,103		283,000
Financing Receivable, Revolving Converted to Term Loans	2,651		10,770
Loans and Leases Receivable, Net of Deferred Income	797,580		779,627
Financing Receivable, Allowance for Credit Loss	7,920	9,487	9,052	14,868	11,085	15,835
Agriculture [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	97,908		142,163
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	95,853		90,612
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	82,533		44,434
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	37,066		58,366
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	54,739		58,893
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	102,476		59,396
Financing Receivable, Revolving	259,260		244,135
Financing Receivable, Revolving Converted to Term Loans	1,744		9,299
Loans and Leases Receivable, Net of Deferred Income	731,579		707,298
Agriculture [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	109		0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,593		90
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	738		285
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	325		33
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	64		0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0		0
Financing Receivable, Revolving	4,526		85
Financing Receivable, Revolving Converted to Term Loans	0		13
Loans and Leases Receivable, Net of Deferred Income	10,355		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	6,343		12,480
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	10,045		5,868
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,643		4,258
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3,862		284
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,529		3,502
Financing Receivable, Revolving	30,317		38,780
Financing Receivable, Revolving Converted to Term Loans	907		1,458
Loans and Leases Receivable, Net of Deferred Income	55,646		71,823
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	115,216		134,693
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	101,292		84,706
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	38,091		10,066
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	6,699		3,498
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3,448		763
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	4,951		1,861
Financing Receivable, Revolving	30,302		29,323
Financing Receivable, Revolving Converted to Term Loans	304		3,753
Loans and Leases Receivable, Net of Deferred Income	300,303		268,663
Financing Receivable, Allowance for Credit Loss	6,559	6,551	7,636	7,953	8,845	8,571
Construction [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	115,216		134,693
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	101,292		66,974
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	19,352		10,066
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	6,699		3,498
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	3,448		763
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	4,897		1,805
Financing Receivable, Revolving	30,302		29,323
Financing Receivable, Revolving Converted to Term Loans	304		3,753
Loans and Leases Receivable, Net of Deferred Income	281,510		250,875
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	18,739		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	54		56
Financing Receivable, Revolving	0		0
Financing Receivable, Revolving Converted to Term Loans	0		0
Loans and Leases Receivable, Net of Deferred Income	18,793		17,788
One-to-Four Family Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	130,355		161,021
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	148,576		78,605
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	60,122		63,255
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	49,345		30,903
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	24,324		21,233
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	83,250		80,261
Financing Receivable, Revolving	227,402		244,330
Financing Receivable, Revolving Converted to Term Loans	777		3,962
Loans and Leases Receivable, Net of Deferred Income	724,151		683,570
Financing Receivable, Allowance for Credit Loss	16,519	15,638	16,875	23,711	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	130,355		161,021
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	146,145		77,756
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	58,921		62,696
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	49,106		29,737
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	23,838		20,889
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	81,118		78,098
Financing Receivable, Revolving	227,230		243,325
Financing Receivable, Revolving Converted to Term Loans	622		3,655
Loans and Leases Receivable, Net of Deferred Income	717,335		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	2,350		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	314		0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0		195
Financing Receivable, Revolving	0		0
Financing Receivable, Revolving Converted to Term Loans	0		0
Loans and Leases Receivable, Net of Deferred Income	2,664		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	81		849
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,201		227
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	239		1,166
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	172		344
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,132		1,968
Financing Receivable, Revolving	172		1,005
Financing Receivable, Revolving Converted to Term Loans	155		307
Loans and Leases Receivable, Net of Deferred Income	4,152		5,866
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	4,289		5,578
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,319		3,109
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,308		3,886
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,789		994
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	673		244
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,124		1,230
Financing Receivable, Revolving	18,029		19,964
Financing Receivable, Revolving Converted to Term Loans	192		514
Loans and Leases Receivable, Net of Deferred Income	31,723		35,519
Financing Receivable, Allowance for Credit Loss	1,186	$ 1,163	1,393	$ 1,595	$ 1,644	$ 883
Consumer Loan [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	4,289		5,548
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,294		3,109
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,270		3,886
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,789		989
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	671		244
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,122		1,060
Financing Receivable, Revolving	18,006		19,911
Financing Receivable, Revolving Converted to Term Loans	192		474
Loans and Leases Receivable, Net of Deferred Income	31,633		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	25		0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	38		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	2		0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2		170
Financing Receivable, Revolving	23		53
Financing Receivable, Revolving Converted to Term Loans	0		40
Loans and Leases Receivable, Net of Deferred Income	$ 90		$ 298