Loans, Credit Scores by Loan Class, Mortgage and Installment Segments (Details) - USD ($) $ in Thousands		3 Months Ended					9 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Loan ratings/credit scores by loan class [Abstract]
Accrued interest included in total			$ 8,436				$ 8,436		$ 8,538
Other Real Estate and Foreclosed Assets [Abstract]
Foreclosed residential real estate properties			1,200				1,200		1,200
Retail mortgage loans in process of foreclosure			200				200		300
Sale of Mortgage Loans [Abstract]
Proceeds from sale of mortgage loan							50,516	$ 27,577
Net gain (loss) on mortgage loans			5,677		$ 2,745		13,590	8,571
Transfer of portfolio loans to loans held for sale							36,622	$ 27,577
Fixed Rate Residential Mortgage and Adjustable Rate Residential Mortgage [Member]
Sale of Mortgage Loans [Abstract]
Proceeds from sale of mortgage loan			9,900		11,100	$ 16,500
Net gain (loss) on mortgage loans			70		$ (10)	$ 50
Residential Adjustable Rate Mortgage Loans [Member]
Sale of Mortgage Loans [Abstract]
Proceeds from sale of mortgage loan				$ 40,600
Net gain (loss) on mortgage loans				10
Residential Fixed Rate Mortgage Loans [Member]
Sale of Mortgage Loans [Abstract]
Transfer of portfolio loans to loans held for sale			36,600
Residential Fixed Rate Mortgage Loans [Member] | Freddie Mac [Member]
Sale of Mortgage Loans [Abstract]
Proceeds from sale of mortgage loan				29,800
Net gain (loss) on mortgage loans				$ 530
Residential Fixed Rate Mortgage Loans [Member] | Freddie Mac [Member] | Subsequent Event [Member]
Sale of Mortgage Loans [Abstract]
Net gain (loss) on mortgage loans		$ 1,000
Mortgage [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		131,420				131,420		121,012
750-799	[1]		485,479				485,479		476,484
700-749	[1]		261,670				261,670		252,126
650-699	[1]		108,985				108,985		114,460
600-649	[1]		37,924				37,924		41,748
550-599	[1]		20,125				20,125		17,301
500-549	[1]		12,994				12,994		9,789
Under 500	[1]		4,424				4,424		3,155
Unknown	[1]		11,314				11,314		10,912
Total	[1]		1,074,335				1,074,335		1,046,987
Accrued interest included in total	[1]		4,300				4,300		4,097
Mortgage [Member] | 1-4 Family [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		101,927				101,927		94,492
750-799	[1]		385,243				385,243		384,344
700-749	[1]		204,241				204,241		202,440
650-699	[1]		84,458				84,458		91,847
600-649	[1]		30,819				30,819		34,342
550-599	[1]		16,410				16,410		13,771
500-549	[1]		10,972				10,972		8,439
Under 500	[1]		3,718				3,718		2,533
Unknown	[1]		9,300				9,300		8,236
Total	[1]		847,088				847,088		840,444
Accrued interest included in total	[1]		3,327				3,327		3,079
Mortgage [Member] | Resort Lending [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		11,151				11,151		10,898
750-799	[1]		31,372				31,372		36,542
700-749	[1]		15,323				15,323		17,282
650-699	[1]		7,612				7,612		9,945
600-649	[1]		2,241				2,241		3,088
550-599	[1]		1,171				1,171		1,867
500-549	[1]		620				620		106
Under 500	[1]		80				80		143
Unknown	[1]		1,256				1,256		1,910
Total	[1]		70,826				70,826		81,781
Accrued interest included in total	[1]		343				343		363
Mortgage [Member] | Home Equity - 1st Lien [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		6,165				6,165		6,784
750-799	[1]		16,300				16,300		17,303
700-749	[1]		9,209				9,209		9,155
650-699	[1]		3,747				3,747		3,987
600-649	[1]		668				668		959
550-599	[1]		663				663		427
500-549	[1]		330				330		418
Under 500	[1]		254				254		98
Unknown	[1]		0				0		113
Total	[1]		37,336				37,336		39,244
Accrued interest included in total	[1]		166				166		199
Mortgage [Member] | Home Equity - 2nd Lien [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		12,177				12,177		8,838
750-799	[1]		52,564				52,564		38,295
700-749	[1]		32,897				32,897		23,249
650-699	[1]		13,168				13,168		8,681
600-649	[1]		4,196				4,196		3,359
550-599	[1]		1,881				1,881		1,236
500-549	[1]		1,072				1,072		826
Under 500	[1]		372				372		381
Unknown	[1]		758				758		653
Total	[1]		119,085				119,085		85,518
Accrued interest included in total	[1]		464				464		456
Installment [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		61,616				61,616		48,026
750-799	[1]		248,817				248,817		208,972
700-749	[1]		100,357				100,357		87,978
650-699	[1]		28,923				28,923		28,162
600-649	[1]		7,849				7,849		7,668
550-599	[1]		3,143				3,143		3,360
500-549	[1]		1,855				1,855		1,775
Under 500	[1]		486				486		548
Unknown	[1]		11,479				11,479		9,690
Total	[1]		464,525				464,525		396,179
Accrued interest included in total	[1]		1,131				1,131		1,030
Installment [Member] | Home Equity - 1st Lien [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		380				380		555
750-799	[1]		1,104				1,104		1,502
700-749	[1]		1,323				1,323		1,582
650-699	[1]		1,399				1,399		1,606
600-649	[1]		934				934		996
550-599	[1]		526				526		759
500-549	[1]		299				299		384
Under 500	[1]		18				18		51
Unknown	[1]		0				0		2
Total	[1]		5,983				5,983		7,437
Accrued interest included in total	[1]		21				21		28
Installment [Member] | Home Equity - 2nd Lien [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		219				219		235
750-799	[1]		1,265				1,265		1,642
700-749	[1]		1,123				1,123		1,682
650-699	[1]		1,104				1,104		1,217
600-649	[1]		678				678		1,272
550-599	[1]		457				457		658
500-549	[1]		208				208		229
Under 500	[1]		50				50		6
Unknown	[1]		15				15		103
Total	[1]		5,119				5,119		7,044
Accrued interest included in total	[1]		16				16		25
Installment [Member] | Boat Lending [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		29,581				29,581		20,767
750-799	[1]		120,085				120,085		100,191
700-749	[1]		42,869				42,869		35,455
650-699	[1]		10,536				10,536		10,581
600-649	[1]		1,783				1,783		1,657
550-599	[1]		808				808		652
500-549	[1]		455				455		286
Under 500	[1]		223				223		266
Unknown	[1]		0				0		39
Total	[1]		206,340				206,340		169,894
Accrued interest included in total	[1]		467				467		403
Installment [Member] | Recreational Vehicle Lending [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		24,296				24,296		20,197
750-799	[1]		90,692				90,692		74,154
700-749	[1]		29,990				29,990		24,890
650-699	[1]		5,560				5,560		4,918
600-649	[1]		1,692				1,692		992
550-599	[1]		617				617		453
500-549	[1]		145				145		225
Under 500	[1]		39				39		7
Unknown	[1]		0				0		0
Total	[1]		153,031				153,031		125,836
Accrued interest included in total	[1]		350				350		311
Installment [Member] | Other [Member]
Loan ratings/credit scores by loan class [Abstract]
800 and above	[1]		7,140				7,140		6,272
750-799	[1]		35,671				35,671		31,483
700-749	[1]		25,052				25,052		24,369
650-699	[1]		10,324				10,324		9,840
600-649	[1]		2,762				2,762		2,751
550-599	[1]		735				735		838
500-549	[1]		748				748		651
Under 500	[1]		156				156		218
Unknown	[1]		11,464				11,464		9,546
Total	[1]		94,052				94,052		85,968
Accrued interest included in total	[1]		$ 277				$ 277		$ 263

[1] Credit scores have been updated within the last twelve months.