Employee Benefit Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Officer cash bonus target minimum	35.00%
Officer cash bonus target maximum	135.00%
Officer cash bonus performance factor minimum	0.00%
Officer cash bonus performance factor maximum	200.00%
Other management cash bonus target minimum	6.00%
Other management cash bonus target maximum	30.00%
Outstanding stock options and warrants	611,518	655,822
Possible future share issuance authorized under equity incentive plans	2,188,696	2,404,131
Total shares reserved for future issuance	2,800,214	3,059,953
Possible future share issuance authorized under equity incentive plan restricted stock	600,000
Stock-based compensation expense	$ 7,466	$ 6,692	$ 6,251
Total unrecognized stock-based compensation costs	$ 4,700
Weighted average remaining term of vesting periods (in years)	2 years 2 months 20 days
401(k) Savings Plan [Abstract]
401(k) employer match percentage	75.00%
401(k) employer match salary limit percentage	6.00%
401(k) employer contribution	$ 1,400	1,400	1,300
Retirement Plan [Abstract]
Retirement plan qualification years of service (in years)	30 years
Retirement plan qualification age	55 years
Retirement plan qualification minimum years of service (in years)	10 years
Retirement plan immediate vesting percentage	100.00%
Deferred Compensation [Abstract]
Marketable securities of non-qualified deferred compensation plan fair value disclosure	$ 1,849	2,388	2,451
Non Qualified Deferred Compensation Obligation Fair Value Disclosure [Roll Forward]
Beginning deferred compensation liability	2,388	2,451	2,736
Mark to market adjustment to deferred compensation (in general and administrative expenses)	(182)	492	222
Distributions from deferred compensation plans	(357)	(555)	(507)
Ending deferred compensation liability	$ 1,849	$ 2,388	$ 2,451
Employee Stock Purchase Plan [Abstract]
Employee stock purchase plan salary limit percentage	25.00%
Employee stock purchase plan market percentage	85.00%
Number of days at end of quarter used to calculate ESPP discount	5 days
Shares of Common Stock issued under the employee stock purchase plans	38,951	33,278	27,773
Discount percentage on newly issues shares	15.00%
Discount on newly issued shares expensed as additional compensation	$ 300	$ 200	$ 200
2015 Plan [Member]
Restricted Stock Activity Rollforward [Abstract]
Awarded and issued (in shares)
Vested (in shares)
Forfeited (in shares)	(13,707)
2014 Plan [Member]
Restricted Stock Activity Rollforward [Abstract]
Awarded and issued (in shares)		34,669
Vested (in shares)		(34,669)
2013 Plan [Member]
Restricted Stock Activity Rollforward [Abstract]
Awarded and issued (in shares)			6,647
Vested (in shares)			(6,647)
Stock Options [Member]
Stock Option Activity Rollforward [Abstract]
Balance of options outstanding (in shares)	640,822	587,115	687,228
Options granted (in shares)		168,748	244,664
Options canceled (in shares)			(14,743)
Options exercised (in shares)	(44,304)	(115,041)	(330,034)
Balance of options outstanding (in shares)	596,518	640,822	587,115
Stock Option Activity, Weighted Average Exercise Price Rollforward [Abstract]
Options outstanding, weighted average exercise price (in dollars per share)	$ 45.29	$ 42.26	$ 37.97
Options granted, weighted average exercise price (in dollars per share)		52.49	43.55
Options canceled, weighted average exercise price (in dollars per share)			42.64
Options exercised, weighted average exercise price (in dollars per share)	40.15	40.41	34.26
Options outstanding, weighted average exercise price (in dollars per share)	$ 45.67	$ 45.29	$ 42.26
Weighted average remaining life of outstanding options (in years)	6 years 9 months 20 days
Options exercisable (in shares)	303,674
Weighted average exercise price (in dollars per share)	$ 43.67
Weighted average remaining life (in years)	6 years 2 months 12 days
Intrinsic value	$ 100
Amount of exercisable options with prices higher than the market price of Company Common Stock	217,386
Cash received or receivable from options exercised	$ 1,900	$ 5,200	$ 13,400
Total instrinsic value of options exercised	400	1,300	4,800
Total intrinsic value of options outstanding	$ 100	$ 3,900	$ 5,100
Prior to 2005 and after 2013 Stock Options [Member]
Retirement Benefits [Abstract]
Vesting term of stock options issued/Period for absolute total return of restricted stock issued (in years)	4 years
Option expiration period (in years)	10 years
Grant date fair value of each stock option granted (in dollars per option)
Assumptions Used in Determining Fair Values of Options/Restricted Stock Granted:
Risk free interest rate
Common stock dividend yield
Expected volatility rate
Average expected option life (in years)
Dividends paid for previous year	1 year
2005 to 2013 Stock Options [Member]
Retirement Benefits [Abstract]
Vesting term of stock options issued/Period for absolute total return of restricted stock issued (in years)	4 years
Option expiration period (in years)	7 years
Grant date fair value of each stock option granted (in dollars per option)		$ 6.72	$ 4.61
Assumptions Used in Determining Fair Values of Options/Restricted Stock Granted:
Risk free interest rate		2.00%	1.40%
Common stock dividend yield		3.40%	3.90%
Expected volatility rate		19.50%	19.70%
Average expected option life (in years)		5 years 9 months	5 years 9 months
Time-Based Restricted Stock [Member]
Retirement Benefits [Abstract]
Vesting term of stock options issued/Period for absolute total return of restricted stock issued (in years)	4 years
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding (in shares)	172,246	188,981	204,720
Awarded and issued (in shares)	94,984	61,404	72,698
Vested (in shares)	(73,307)	(78,139)	(84,212)
Forfeited (in shares)	(2,684)		(4,225)
Balance of restricted stock outstanding (in shares)	191,239	172,246	188,981
Restricted Stock Activity, Weighted Average Grant Date Fair Value Rollforward [Abstract]
Restricted stock outstanding, weighted average grant date fair value (in dollars per share)	$ 46.46	$ 42.06	$ 39.74
Awarded and issued, weighted average grant date fair value (in dollars per share)	43.01	52.49	43.59
Vested, weighted average grant date fair value (in dollars per share)	44.19	40.55	37.76
Forfeited, weighted average grant date fair value (in dollars per share)	45.89		41.96
Restricted stock outstanding, weighted average grant date fair value (in dollars per share)	45.62	46.46	42.06
Grant date fair value of restricted stock (in dollars per share)	$ 43.01	$ 52.49	$ 43.59
Fair value at grant date of restricted stock issued	$ 4,100	$ 3,200	$ 3,200
Vesting date fair value of restricted stock	$ 3,200	$ 4,100	$ 3,700
Total Return-Based Restricted Stock [Member]
Retirement Benefits [Abstract]
Vesting term of stock options issued/Period for absolute total return of restricted stock issued (in years)	3 years
Assumptions Used in Determining Fair Values of Options/Restricted Stock Granted:
Risk free interest rate	2.30%	1.60%	0.90%
Common stock dividend yield	3.90%	3.50%	4.10%
Expected volatility rate	41.10%	42.80%	43.10%
Dividends paid for previous year	1 year
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding (in shares)	160,724	183,724	195,303
Awarded and issued (in shares)	77,456	84,013	64,701
Vested (in shares)	(41,160)	(107,013)	(71,617)
Forfeited (in shares)	(16,926)		(4,663)
Balance of restricted stock outstanding (in shares)	180,094	160,724	183,724
Restricted Stock Activity, Weighted Average Grant Date Fair Value Rollforward [Abstract]
Restricted stock outstanding, weighted average grant date fair value (in dollars per share)	$ 44.72	$ 39.82	$ 36.66
Awarded and issued, weighted average grant date fair value (in dollars per share)	40.81	44.76	40.87
Vested, weighted average grant date fair value (in dollars per share)	45.61	37.88	36.50
Forfeited, weighted average grant date fair value (in dollars per share)	45.24		39.91
Restricted stock outstanding, weighted average grant date fair value (in dollars per share)	$ 43.34	$ 44.72	$ 39.82
Percentage of return-based restricted stock issued to officers that will vest, minimum	0.00%	0.00%	0.00%
Percentage of return-based restricted stock issued to officers that will vest, maximum	150.00%	150.00%	150.00%
Company total return, total return-based restricted stock	100.00%
Vesting percentage, total return-based restricted stock	75.00%	75.00%	75.00%
Grant date fair value of restricted stock (in dollars per share)	$ 40.81	$ 44.76	$ 40.87
Fair value at grant date of restricted stock issued	$ 3,200	$ 2,400	$ 2,400
Vesting date fair value of restricted stock	$ 1,800	$ 5,600	$ 3,100
Period preceding date of grant	3 months
Total Return-Based Restricted Stock Current Year Issuance [Member]
Restricted Stock Activity, Weighted Average Grant Date Fair Value Rollforward [Abstract]
Awarded and issued, weighted average grant date fair value (in dollars per share)	$ 40.81	$ 49.59	$ 41.37
Grant date fair value of restricted stock (in dollars per share)	$ 40.81	$ 49.59	$ 41.37