Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
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	1,144,309		1,224,455
Possible future share issuance authorized under equity incentive plan	2,047,550		2,363,695
Total shares reserved for future issuance	3,191,859		3,588,150
Possible future share issuance authorized under equity incentive plan restricted stock	600,000
Possible future share issuance authorized under charter	119,700,000
Stock-based compensation expense	$ 7,613,000		$ 6,094,000		$ 6,572,000
Total unrecognized stock-based compensation costs	4,500,000
Weighted average remaining term of vesting periods (in years)	2 years 4 months 24 days
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	3,354,000		3,149,000		3,479,000
Units of phantom stock discount	15.00%
Phantom stock dividend discount	15.00%
Non Qualified Deferred Compensation Obligation Fair Value Disclosure [Roll Forward]
Beginning deferred compensation liability	3,149,000		4,091,000		6,898,000
Contributions to deferred compensation plans	0		545,000		229,000
Mark to market adjustment to deferred compensation (in general and administrative expenses)	475,000		(119,000)		246,000
Distributions from deferred compensation plans	(270,000)		(1,368,000)		(3,282,000)
Ending deferred compensation liability	3,354,000		3,149,000		4,091,000
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	1,000,000		1,100,000		1,000,000
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	34,126		30,826		27,378
Discount on newly issued shares expensed as additional compensation	200,000		200,000		100,000
Stock Options [Member]
Stock Option Activity Rollforward [Abstract]
Balance of options outstanding	1,209,455	[1],[2]	1,480,196		1,467,773
Options granted	190,886		146,581		190,826
Options exercised	(271,032)		(417,322)		(178,403)
Balance of options outstanding	1,129,309		1,209,455	[1],[2]	1,480,196
Options outstanding, weighted average exercise price	$ 29.08	[1],[2]	$ 27.95		$ 27.15
Options granted, weighted average exercise price	$ 31.97		$ 33.93		$ 29.05
Options exercised, weighted average exercise price	$ 26.87		$ 26.79		$ 22.54
Options outstanding, weighted average exercise price	$ 30.10		$ 29.08	[1],[2]	$ 27.95
Weighted average remaining life of outstanding options	3 years 4 months
Options exercisable	634,550
Weighted average exercise price	$ 30.75
Weighted average remaining life	2 years 1 month 12 days
Intrinsic value	2,600,000
Amount of exercisable options with prices higher than the market price of Company Common Stock	173,007
Cash received or receivable from options exercised	7,400,000		11,900,000		4,400,000
Total instrinsic value of options exercised	1,900,000		3,000,000		1,700,000
Total intrinsic value of options outstanding	5,000,000		3,300,000		7,200,000
Prior to 2005 Stock Options [Member]
Compensation and Retirement Disclosure [Abstract]
Vesting term of stock options issued (in years)	4 years
Option expiration period (in years)	10 years
Stock Option Activity Rollforward [Abstract]
Period for absolute total return (in years)	4 years
2005 and Subsequent Stock Options [Member]
Compensation and Retirement Disclosure [Abstract]
Vesting term of stock options 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)	$ 5.47		$ 6.47		$ 4.96
Assumptions Used in Determining Fair Values of Options Granted:
Risk free interest rate	1.10%	[3]	2.40%	[3]	2.60%	[3]
Common stock dividend yield	5.30%	[4]	5.00%	[4]	5.90%	[4]
Expected volatility rate	33.40%	[5]	32.50%	[5]	32.20%	[5]
Average expected option life (in years)	5 years 9 months	[6]	5 years 9 months	[6]	5 years 9 months	[6]
Dividends paid for previous year	1 year
Stock Option Activity Rollforward [Abstract]
Period for absolute total return (in years)	4 years
Time-Based Restricted Stock [Member]
Stock Option Activity Rollforward [Abstract]
Percentage of employees restricted stock vested per anniversary date	25.00%
Percentage of directors time-based restricted stock that vest each year after grant date	25.00%
Grant date fair value of restricted stock	$ 32.27	[7]	$ 33.70	[7]	$ 29.05	[7]
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding	224,661		264,326		316,074
Awarded and issued	90,983	[7]	76,966	[7]	88,930	[7]
Vested	(92,239)	[8]	(116,631)	[8]	(138,745)	[8]
Forfeited	(903)				(1,933)
Balance of restricted stock outstanding	222,502		224,661		264,326
Restricted stock outstanding, weighted average grant date fair value	$ 28.02		$ 27.08		$ 28.60
Awarded and issued, weighted average grant date fair value	$ 32.27	[7]	$ 33.70	[7]	$ 29.05	[7]
Vested, weighted average grant date fair value	$ 27.14	[8]	$ 30.64	[8]	$ 31.81	[8]
Forfeited, weighted average grant date fair value	$ 30.12				$ 25.86
Restricted stock outstanding, weighted average grant date fair value	$ 30.31		$ 28.02		$ 27.08
Fair value at grant date of restricted stock issued	2,900,000		2,600,000		2,600,000
Vesting date fair value of restricted stock	2,900,000		3,900,000		4,300,000
Total Return-Based Restricted Stock [Member]
Compensation and Retirement Disclosure [Abstract]
Vesting term of stock options issued (in years)	3 years
Assumptions Used in Determining Fair Values of Options Granted:
Risk free interest rate	0.40%	[9]	0.97%	[9]	1.32%	[9]
Common stock dividend yield	5.40%	[4]	5.42%	[4]	5.55%	[4]
Expected volatility rate	43.70%	[10]	42.80%	[10]	42.50%	[10]
Dividends paid for previous year	1 year
Stock Option Activity Rollforward [Abstract]
Percentage of return-based restricted stock issued to officers that will vest, minimum	0.00%
Percentage of return-based restricted stock issued to officers that will vest, maximum	250.00%
Period for absolute total return (in years)	3 years
Grant date fair value of restricted stock	$ 38.71	[11]	$ 41.02	[11]	$ 29.05	[11]
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding	122,829		231,835		202,775
Awarded and issued	67,902	[11]	57,386	[11]	77,624	[11]
Vested	(32,722)	[12]	(66,417)	[12]	(47,257)	[12]
Forfeited	(32,721)		(99,975)		(1,307)
Balance of restricted stock outstanding	125,288		122,829		231,835
Restricted stock outstanding, weighted average grant date fair value	$ 34.86		$ 21.03		$ 22.05
Awarded and issued, weighted average grant date fair value	$ 38.71	[11]	$ 41.02	[11]	$ 29.05	[11]
Vested, weighted average grant date fair value	$ 29.47	[12]	$ 13.79	[12]	$ 38.50	[12]
Forfeited, weighted average grant date fair value	$ 29.47		$ 13.79		$ 22.99
Restricted stock outstanding, weighted average grant date fair value	$ 32.87		$ 34.86		$ 21.03
Fair value at grant date of restricted stock issued	2,600,000		2,400,000		2,300,000
Vesting date fair value of restricted stock	1,100,000		2,000,000		1,600,000
Partnership [Member]
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	1,144,309		1,224,455
Possible future share issuance authorized under equity incentive plan	2,047,550		2,363,695
Total shares reserved for future issuance	3,191,859		3,588,150
Possible future share issuance authorized under equity incentive plan restricted stock	600,000
Possible future share issuance authorized under charter	119,700,000
Stock-based compensation expense	7,613,000		6,094,000		6,572,000
Total unrecognized stock-based compensation costs	4,500,000
Weighted average remaining term of vesting periods (in years)	2 years 4 months 24 days
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	3,354,000		3,149,000		3,479,000
Units of phantom stock discount	15.00%
Phantom stock dividend discount	15.00%
Non Qualified Deferred Compensation Obligation Fair Value Disclosure [Roll Forward]
Beginning deferred compensation liability	3,149,000		4,091,000		6,898,000
Contributions to deferred compensation plans	0		545,000		229,000
Mark to market adjustment to deferred compensation (in general and administrative expenses)	475,000		(119,000)		246,000
Distributions from deferred compensation plans	(270,000)		(1,368,000)		(3,282,000)
Ending deferred compensation liability	3,354,000		3,149,000		4,091,000
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	1,000,000		1,100,000		1,000,000
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	34,126		30,826		27,378
Discount on newly issued shares expensed as additional compensation	200,000		200,000		100,000
Partnership [Member] | Stock Options [Member]
Stock Option Activity Rollforward [Abstract]
Balance of options outstanding	1,209,455	[1],[2]	1,480,196		1,467,773
Options granted	190,886		146,581		190,826
Options exercised	(271,032)		(417,322)		(178,403)
Balance of options outstanding	1,129,309		1,209,455	[1],[2]	1,480,196
Options outstanding, weighted average exercise price	$ 29.08	[1],[2]	$ 27.95		$ 27.15
Options granted, weighted average exercise price	$ 31.97		$ 33.93		$ 29.05
Options exercised, weighted average exercise price	$ 26.87		$ 26.79		$ 22.54
Options outstanding, weighted average exercise price	$ 30.10		$ 29.08	[1],[2]	$ 27.95
Weighted average remaining life of outstanding options	3 years 4 months
Options exercisable	634,550
Weighted average exercise price	$ 30.75
Weighted average remaining life	2 years 1 month 12 days
Intrinsic value	2,600,000
Amount of exercisable options with prices higher than the market price of Company Common Stock	173,007
Cash received or receivable from options exercised	7,400,000		11,900,000		4,400,000
Total instrinsic value of options exercised	1,900,000		3,000,000		1,700,000
Total intrinsic value of options outstanding	5,000,000		3,300,000		7,200,000
Partnership [Member] | Prior to 2005 Stock Options [Member]
Compensation and Retirement Disclosure [Abstract]
Vesting term of stock options issued (in years)	4 years
Option expiration period (in years)	10 years
Stock Option Activity Rollforward [Abstract]
Period for absolute total return (in years)	4 years
Partnership [Member] | 2005 and Subsequent Stock Options [Member]
Compensation and Retirement Disclosure [Abstract]
Vesting term of stock options 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)	$ 5.47		$ 6.47		$ 4.96
Assumptions Used in Determining Fair Values of Options Granted:
Risk free interest rate	1.10%	[3]	2.43%	[3]	2.58%	[3]
Common stock dividend yield	5.30%	[4]	5.01%	[4]	5.85%	[4]
Expected volatility rate	33.40%	[5]	32.50%	[5]	32.20%	[5]
Average expected option life (in years)	5 years 9 months	[6]	5 years 9 months	[6]	5 years 9 months	[6]
Dividends paid for previous year	1 year
Stock Option Activity Rollforward [Abstract]
Period for absolute total return (in years)	4 years
Partnership [Member] | Time-Based Restricted Stock [Member]
Stock Option Activity Rollforward [Abstract]
Percentage of employees restricted stock vested per anniversary date	25.00%
Percentage of directors time-based restricted stock that vest each year after grant date	25.00%
Grant date fair value of restricted stock	$ 32.27	[7]	$ 33.70	[7]	$ 29.05	[7]
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding	224,661		264,326		316,074
Awarded and issued	90,983	[7]	76,966	[7]	88,930	[7]
Vested	(92,239)	[8]	(116,631)	[8]	(138,745)	[8]
Forfeited	(903)				(1,933)
Balance of restricted stock outstanding	222,502		224,661		264,326
Restricted stock outstanding, weighted average grant date fair value	$ 28.02		$ 27.08		$ 28.60
Awarded and issued, weighted average grant date fair value	$ 32.27	[7]	$ 33.70	[7]	$ 29.05	[7]
Vested, weighted average grant date fair value	$ 27.14	[8]	$ 30.64	[8]	$ 31.81	[8]
Forfeited, weighted average grant date fair value	$ 30.12				$ 25.86
Restricted stock outstanding, weighted average grant date fair value	$ 30.31		$ 28.02		$ 27.08
Fair value at grant date of restricted stock issued	2,900,000		2,600,000		2,600,000
Vesting date fair value of restricted stock	2,900,000		3,900,000		4,300,000
Partnership [Member] | Total Return-Based Restricted Stock [Member]
Compensation and Retirement Disclosure [Abstract]
Vesting term of stock options issued (in years)	3 years
Assumptions Used in Determining Fair Values of Options Granted:
Risk free interest rate	0.40%	[9]	1.00%	[9]	1.30%	[9]
Common stock dividend yield	5.40%	[4]	5.40%	[4]	5.60%	[4]
Expected volatility rate	43.70%	[10]	42.80%	[10]	42.50%	[10]
Dividends paid for previous year	1 year
Stock Option Activity Rollforward [Abstract]
Percentage of return-based restricted stock issued to officers that will vest, minimum	0.00%
Percentage of return-based restricted stock issued to officers that will vest, maximum	250.00%
Period for absolute total return (in years)	3 years
Grant date fair value of restricted stock	$ 38.71	[11]	$ 41.02	[11]	$ 29.05	[11]
Restricted Stock Activity Rollforward [Abstract]
Balance of restricted stock outstanding	122,829		231,835		202,775
Awarded and issued	67,902	[11]	57,386	[11]	77,624	[11]
Vested	(32,722)	[12]	(66,417)	[12]	(47,257)	[12]
Forfeited	(32,721)		(99,975)		(1,307)
Balance of restricted stock outstanding	125,288		122,829		231,835
Restricted stock outstanding, weighted average grant date fair value	$ 34.86		$ 21.03		$ 22.05
Awarded and issued, weighted average grant date fair value	$ 38.71	[11]	$ 41.02	[11]	$ 29.05	[11]
Vested, weighted average grant date fair value	$ 29.47	[12]	$ 13.79	[12]	$ 38.50	[12]
Forfeited, weighted average grant date fair value	$ 29.47		$ 13.79		$ 22.99
Restricted stock outstanding, weighted average grant date fair value	$ 32.87		$ 34.86		$ 21.03
Fair value at grant date of restricted stock issued	2,600,000		2,400,000		2,300,000
Vesting date fair value of restricted stock	$ 1,100,000		$ 2,000,000		$ 1,600,000

[1] The outstanding options at December 31, 2012 had a weighted average remaining life of 3.3 years.

[2] We have 634,550 options exercisable at December 31, 2012 with a weighted average exercise price of $30.75, weighted average remaining life of 2.1 years and intrinsic value of $2.6 million. Of these exercisable options, 173,007 had exercise prices higher than the market price of our Common Stock at December 31, 2012.

[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 our historical data.

[7] The fair value at grant date of time-based restricted stock issued during the years ended December 31, 2012, 2011 and 2010 was $2.9 million, $2.6 million and $2.6 million, respectively.

[8] The vesting date fair value of time-based restricted stock that vested during the years ended December 31, 2012, 2011 and 2010 was $2.9 million, $3.9 million and $4.3 million, respectively.

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

[11] The fair value at grant date of total return-based restricted stock issued during the years ended December 31, 2012, 2011 and 2010 was $2.6 million, $2.4 million and $2.3 million, respectively. There were no performance-based restricted stock issued subsequent to 2008.

[12] The vesting date fair value of total return-based and other types of performance-based restricted stock that vested during the years ended December 31, 2012, 2011 and 2010 was $1.1 million, $2.0 million and $1.6 million, respectively.