Employee Benefits, Stock-Based Compensation (Details)		1 Months Ended	12 Months Ended
		Jan. 31, 2016 shares	Dec. 31, 2020 USD ($) Plan $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares		Dec. 31, 2018 USD ($) $ / shares shares
Stock-based Compensation [Abstract]
Number of active incentive stock option plan | Plan			1
Number of inactive incentive stock option plan | Plan			1
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Shares available for future issuance (in shares)			460,000
Unrecognized compensation cost, grant date fair value of vested shares, cash received from option exercises, and actual tax benefit realized [Abstract]
Unrecognized compensation cost of unvested share-based compensation arrangements granted under the plan at year-end | $			$ 1,512,000	$ 1,410,000		$ 1,072,000
Grant date fair value of shares vested for the year | $			887,000	605,000		645,000
Cash received from option exercises under all share-based payment arrangements for the year | $			11,000	401,000		399,000
Tax benefit realized for the tax deductions from option exercises of the share-based payment arrangements for the year | $			$ 1,000	$ 27,000		$ 49,000
Expected period for recognition of unrecognized compensation cost			2 years 6 months
Stock Options [Member]
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Number of shares to be issued upon exercise (in shares)			20,000
Weighted average price (in dollars per share) | $ / shares			$ 32.27
Grants (in shares)			0	0		0
Shares available for future issuance (in shares)	[1]		460,000
Restricted Stock [Member]
Stock-based Compensation [Abstract]
Shares authorized (in shares)			550,000
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Number of shares to be issued upon exercise (in shares)	[2]
Weighted average price (in dollars per share) | $ / shares	[3]
Maximum number of shares to be grant to a participant (in shares)			75,000
Shares available for future issuance (in shares)	[1]
Performance Units [Member]
Stock-based Compensation [Abstract]
Number of shares issued to date (in shares)			0
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Number of shares to be issued upon exercise (in shares)	[4]
Weighted average price (in dollars per share) | $ / shares	[3]
Maximum amount of shares to be grant to a participant | $			$ 1,000,000
Shares available for future issuance (in shares)	[1]
Stock Appreciation Rights (SARs) [Member]
Stock-based Compensation [Abstract]
Number of shares issued to date (in shares)			0
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Number of shares to be issued upon exercise (in shares)	[5]
Weighted average price (in dollars per share) | $ / shares	[3]
Maximum number of shares to be grant to a participant (in shares)			100,000
Shares available for future issuance (in shares)	[1]
2015 Plan [Member]
Stock-based Compensation [Abstract]
Shares authorized (in shares)			550,000
Number of shares issued to date (in shares)			94,453
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Shares available, beginning of period (in shares)			481,396
Forfeitures (in shares)			0
Shares available for future issuance (in shares)			459,852	481,396
2015 Plan [Member] | Stock Options [Member]
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Grants (in shares)			0	0		0
Number of shares with accelerated vesting (in shares)						10,000
Options, number of shares [Roll Forward]
Outstanding at beginning of year (in shares)			0	0	[6]	10,000	[6]
Granted (in shares)			0	0		0	[6]
Exercised (in shares)			0	0		(10,000)	[6]
Forfeited/expired (in shares)			0	0		0	[6]
Outstanding at end of year (in shares)			0	0		0	[6]
Exercisable at end of year (in shares)			0	0		0	[6]
Options, weighted average exercise price [Abstract]
Outstanding, beginning of period (in dollars per share) | $ / shares			$ 0	$ 0	[6]	$ 33.55	[6]
Granted (in dollars per share) | $ / shares			0	0		0	[6]
Exercised (in dollars per share) | $ / shares			0	0		33.55	[6]
Forfeited/expired (in dollars per share) | $ / shares			0	0		0	[6]
Outstanding, end of period (in dollars per share) | $ / shares			0	0		0	[6]
Exercisable, end of period (in dollars per share) | $ / shares			$ 0	$ 0		$ 0	[6]
Nonvested options, number of shares [Roll Forward]
Granted (in shares)			0	0		0	[6]
Options, additional disclosures [Abstract]
Intrinsic value of options exercised | $			$ 0	$ 0		$ 140,000
Intrinsic value of options exercisable | $			0	0		0
Intrinsic value of outstanding options | $			$ 0	$ 0		$ 0
2015 Plan [Member] | Restricted Stock [Member]
Number of shares to be issued upon exercise of outstanding stock-based awards and remaining shares available for future issuance [Abstract]
Shares issued (in shares)		18,069
Grants (in shares)			(21,544)
Restricted stock activity, grants [Roll Forward]
Outstanding at beginning of year (in shares)			50,992	34,255		33,085
Granted (in shares)			21,544	27,921		11,320
Vested (in shares)			(16,985)	(10,596)		(8,761)
Forfeited (in shares)			0	(588)		(1,389)
Outstanding at end of year (in shares)			55,551	50,992		34,255
Restricted stock activity, weighted average fair value at grant [Roll Forward]
Outstanding at beginning of year (in dollars per share) | $ / shares			$ 43.08	$ 44.46		$ 41.84
Granted (in dollars per share) | $ / shares			44.64	41.12		49.30
Vested (in dollars per share) | $ / shares			41.92	42.39		40.46
Forfeited (in dollars per share) | $ / shares			0	43.04		46.77
Outstanding at end of year (in dollars per share) | $ / shares			$ 44.04	$ 43.08		$ 44.46
2006 Plan [Member] | Stock Options [Member]
Options, number of shares [Roll Forward]
Outstanding at beginning of year (in shares)			20,495	32,571		35,376
Granted (in shares)			0	0		0
Exercised (in shares)			(495)	(12,076)		(2,475)
Forfeited/expired (in shares)			0	0		(330)
Outstanding at end of year (in shares)			20,000	20,495		32,571
Exercisable at end of year (in shares)			20,000	495		2,571
Options, weighted average exercise price [Abstract]
Outstanding, beginning of period (in dollars per share) | $ / shares			$ 32.04	$ 32.47		$ 31.90
Granted (in dollars per share) | $ / shares			0	0		0
Exercised (in dollars per share) | $ / shares			22.81	33.19		25.52
Forfeited/expired (in dollars per share) | $ / shares			0	0		23.79
Outstanding, end of period (in dollars per share) | $ / shares			32.27	32.04		32.47
Exercisable, end of period (in dollars per share) | $ / shares			$ 32.27	$ 22.81		$ 25.11
Nonvested options, number of shares [Roll Forward]
Nonvested, beginning of period (in shares)			20,000
Granted (in shares)			0	0		0
Vested (in shares)			20,000
Forfeited (in shares)			0
Nonvested, end of period (in shares)			0	20,000
Nonvested options, weighted average grant date fair value [Abstract]
Nonvested, beginning of period (in dollars per share) | $ / shares			$ 6.59
Granted (in dollars per share) | $ / shares			0
Vested (in dollars per share) | $ / shares			6.59
Forfeited (in dollars per share) | $ / shares			0
Nonvested, end of period (in dollars per share) | $ / shares			$ 0	$ 6.59
Options, additional disclosures [Abstract]
Weighted average remaining contractual term			4 years 1 month 6 days
Intrinsic value of options exercised | $			$ 11,000	$ 135,000		$ 56,000
Intrinsic value of options exercisable | $			96,000	12,000		37,000
Intrinsic value of outstanding options | $			$ 96,000	$ 299,000		$ 233,000
2006 Plan [Member] | Restricted Stock [Member]
Restricted stock activity, grants [Roll Forward]
Outstanding at beginning of year (in shares)			0	2,064		5,426
Granted (in shares)			0	0		0
Vested (in shares)			0	(2,064)		(3,236)
Forfeited (in shares)			0	0		(126)
Outstanding at end of year (in shares)			0	0		2,064
Restricted stock activity, weighted average fair value at grant [Roll Forward]
Outstanding at beginning of year (in dollars per share) | $ / shares			$ 0	$ 32.27		$ 33.24
Granted (in dollars per share) | $ / shares			0	0		0
Vested (in dollars per share) | $ / shares			0	32.27		33.90
Forfeited (in dollars per share) | $ / shares			0	0		32.27
Outstanding at end of year (in dollars per share) | $ / shares			$ 0.00	$ 0		$ 32.27

[1] Under the 2015 Plan, 550,000 shares are authorized for issuance; 94,453 have been issued as of December 31, 2020  In January of 2016, 18,069 restricted stock shares were issued under the terms of the 2015 Plan pursuant to awards granted under the 2006 Plan.  Additional shares will not be issued pursuant to awards granted from prior plans.

[2] The maximum number of shares of restricted stock that may be granted is 550,000 shares, and the maximum that may be granted to a participant during any calendar year is 75,000 shares.

[3] Not applicable

[4]  No performance units payable in stock had been issued as of December 31, 2020.  The maximum payment that can be made pursuant to performance units granted to any one participant in any calendar year is $1,000,000.

[5]  No SARS have been issued.  The maximum number of shares with respect to which SARs may be granted to a participant during any calendar year is 100,000 shares.

[6] Pursuant to the 2015 Plan provisions, the death of the option holder accelerated the vesting of 10,000 shares in 2018.