Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Officer cash bonus target minimum	30.00%
Officer cash bonus target maximum	130.00%
Officer cash bonus performance factor minimum	0.00%
Officer cash bonus performance factor maximum	200.00%
Other management cash bonus target minimum	10.00%
Other management cash bonus target maximum	30.00%
Number of outstanding options and warrants	592,321		889,382
Possible future share issuance authorized under equity incentive plans	1,382,406		1,742,237
Total shares reserved for future issuance	1,974,727		2,631,619
Possible future share issuance authorized under equity incentive plan restricted stock	300,000
Stock-based compensation expense	$ 6,939,000		$ 6,899,000		$ 7,613,000
Total unrecognized stock-based compensation costs	4,700,000
Weighted average remaining term of vesting periods (in years)	2 years 4 months
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	1,200,000		1,100,000		1,000,000
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
2009 and prior retirement plan immediate vesting percentage	100.00%
Deferred Compensation [Abstract]
Marketable securities of non-qualified deferred compensation plan fair value disclosure	3,635,000		3,996,000		3,354,000
Non Qualified Deferred Compensation Obligation Fair Value Disclosure [Roll Forward]
Beginning deferred compensation liability	3,996,000		3,354,000		3,149,000
Mark to market adjustment to deferred compensation (in general and administrative expenses)	235,000		803,000		475,000
Distributions from deferred compensation plans	(596,000)		(161,000)		(270,000)
Ending deferred compensation liability	3,635,000		3,996,000		3,354,000
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	28,682		27,250		34,126
Employee Stock Purchase Plan Market Percentage Discount	15.00%
Discount on newly issued shares expensed as additional compensation	200,000		200,000		200,000
Stock Options [Member]
Stock Option Activity Rollforward [Abstract]
Balance of options outstanding	874,382	[1],[2]	1,129,309		1,209,455
Options granted	190,330		168,700		190,886
Options canceled	(134,628)
Options exercised	(352,763)		(423,627)		(271,032)
Balance of options outstanding	577,321	[1],[2]	874,382	[1],[2]	1,129,309
Options outstanding, weighted average exercise price	$ 32.24		$ 30.10		$ 29.08
Options granted, weighted average exercise price	$ 37.90		$ 36.50		$ 31.97
Options canceled, weighted average exercise price	$ 41.93
Options exercised, weighted average exercise price	$ 27.21		$ 28.22		$ 26.87
Options outstanding, weighted average exercise price	$ 34.92	[1],[2]	$ 32.24		$ 30.10
Weighted average remaining life of outstanding options	5 years 9 months 20 days
Options exercisable	128,364
Weighted average exercise price	$ 31.44
Weighted average remaining life	3 years 1 month 6 days
Intrinsic value	1,600,000
Cash received or receivable from options exercised	11,100,000		12,500,000		7,400,000
Total instrinsic value of options exercised	5,000,000		3,900,000		1,900,000
Total intrinsic value of options outstanding	5,400,000		4,300,000		5,000,000
Prior to 2005 and 2014 Stock Options [Member]
Compensation and Retirement Disclosure [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)	$ 6.75
Assumptions Used in Determining Fair Values of Options/Restricted Stock Granted:
Risk free interest rate	1.80%	[3]
Common stock dividend yield	4.50%	[4]
Expected volatility rate	30.30%	[5]
Average expected option life (in years)	5 years 9 months	[6]
Dividends paid for previous year	1 year
2005 to 2013 Stock Options [Member]
Compensation and Retirement Disclosure [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)			$ 6.50		$ 5.47
Assumptions Used in Determining Fair Values of Options/Restricted Stock Granted:
Risk free interest rate			1.00%	[3]	1.10%	[3]
Common stock dividend yield			4.70%	[4]	5.30%	[4]
Expected volatility rate			32.40%	[5]	33.40%	[5]
Average expected option life (in years)			5 years 9 months	[6]	5 years 9 months	[6]
Time-Based Restricted Stock [Member]
Compensation and Retirement Disclosure [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	212,796		222,502		224,661
Awarded and issued	94,932	[7]	86,144	[7]	90,983	[7]
Vested	(85,660)	[8]	(94,037)	[8]	(92,239)	[8]
Forfeited	0		(1,813)		(903)
Balance of restricted stock outstanding	222,068		212,796		222,502
Restricted stock outstanding, weighted average grant date fair value	$ 33.96		$ 30.31		$ 28.02
Awarded and issued, weighted average grant date fair value	$ 37.76	[7]	$ 36.64	[7]	$ 32.27	[7]
Vested, weighted average grant date fair value	$ 32.87	[8]	$ 27.80	[8]	$ 27.14	[8]
Forfeited, weighted average grant date fair value	$ 0.00		$ 36.01		$ 30.12
Restricted stock outstanding, weighted average grant date fair value	$ 35.97		$ 33.96		$ 30.31
Grant date fair value of restricted stock	$ 37.76	[7]	$ 36.64	[7]	$ 32.27	[7]
Fair value at grant date of restricted stock issued	3,600,000		3,200,000		2,900,000
Vesting date fair value of restricted stock	3,200,000		3,400,000		2,900,000
Total Return-Based Restricted Stock [Member]
Compensation and Retirement Disclosure [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	0.70%	[9]	0.40%	[9]	0.40%	[9]
Common stock dividend yield	4.70%	[10]	4.90%	[10]	5.40%	[10]
Expected volatility rate	43.40%	[11]	43.40%	[11]	43.70%	[11]
Dividends paid for previous year	1 year
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding	133,388		125,288		122,829
Awarded and issued	74,569	[12]	65,486	[12]	67,902	[12]
Vested	0	[13]	(41,863)	[13]	(32,722)	[13]
Forfeited	0		(15,523)		(32,721)
Balance of restricted stock outstanding	207,957		133,388		125,288
Restricted stock outstanding, weighted average grant date fair value	$ 35.29		$ 32.87		$ 34.86
Awarded and issued, weighted average grant date fair value	$ 35.58	[12]	$ 31.73	[12]	$ 38.71	[12]
Vested, weighted average grant date fair value	$ 0.00	[13]	$ 24.75	[13]	$ 29.47	[13]
Forfeited, weighted average grant date fair value	$ 0.00		$ 24.75		$ 29.47
Restricted stock outstanding, weighted average grant date fair value	$ 35.70		$ 35.29		$ 32.87
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%		250.00%
Company total return, total return-based restricted stock	100.00%
Vesting percentage, total return-based restricted stock	75.00%		50.00%		50.00%
Grant date fair value of restricted stock	$ 35.58	[12]	$ 31.73	[12]	$ 38.71	[12]
Fair value at grant date of restricted stock issued	2,700,000		2,100,000		2,600,000
Vesting date fair value of restricted stock			$ 1,500,000		$ 1,100,000
Period preceding date of grant	0 years 3 months

[1] The Company had 128,364 options exercisable at December 31, 2014 with a weighted average exercise price of $31.44, weighted average remaining life of 3.1 years and intrinsic value of $1.6 million. Of these exercisable options, there were no exercise prices higher than the market price of our Common Stock at December 31, 2014.

[2] The outstanding options at December 31, 2014 had a weighted average remaining life of 5.8 years.

[3] Represents the interest rate as of the grant date on US treasury bonds having the same life as the estimated life of the option grants.

[4] The dividend yield is calculated utilizing the dividends paid for the previous one-year period and the per share price of Common Stock on the date of grant.

[5] Based on the historical volatility of Common Stock over a period relevant to the related stock option grant.

[6] The average expected option life is based on an analysis of the Company's historical data.

[7] The weighted average fair value at grant date of time-based restricted stock issued during the years ended December 31, 2014, 2013 and 2012 was $3.6 million, $3.2 million and $2.9 million, respectively.

[8] The vesting date fair value of time-based restricted stock that vested during the years ended December 31, 2014, 2013 and 2012 was $3.2 million, $3.4 million and $2.9 million, respectively. Vested shares include those shares surrendered by employees to satisfy tax withholding obligations in connection with such vesting.

[9] Represents the interest rate as of the grant date on US treasury bonds having the same life as the estimated life of the total return-based restricted stock grants.

[10] The dividend yield is calculated utilizing the dividends paid for the previous one-year period and the average per share price of Common Stock during the three-month period preceding the date of grant.

[11] Based on the historical volatility of Common Stock over a period relevant to the related total return-based restricted stock grant.

[12] The fair value at grant date of total return-based restricted stock issued during the years ended December 31, 2014, 2013 and 2012 was $2.7 million, $2.1 million and $2.6 million, respectively.

[13] The vesting date fair value of total return-based restricted stock that vested during the years ended December 31, 2013 and 2012 was $1.5 million and $1.1 million, respectively. Vested shares include those shares surrendered by employees to satisfy tax withholding obligations in connection with such vesting. There were no vested shares of total return-based restricted stock during the year ended December 31, 2014.