Stock-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 plan	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans covering employees, officers and directors	5
Expiration period of stock options (in years)	10 years
Employee Benefit Plan
Maximum 401(K) plan contribution by employer as a percent of employee's salary	3.50%
Aggregate employer 401(K) plan contribution during the period	$ 1,036,000	$ 768,000	$ 267,000
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	2 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Executive Deferred Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans for executive officers	1
Number of shares authorized for issuance	500,000
Number of shares available for future issuance	500,000
Nonemployee Directors' Deferred Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans for directors	1
Number of shares authorized for issuance	500,000
Number of shares available for future issuance	424,704
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested awards	1,900,000
Weighted average period over which cost is recognized (in years)	1 year 4 months
Proceeds from options exercised	7,200,000	21,500,000	2,500,000
Fair value assumptions of stock options using Black-Scholes option pricing model
Risk-free interest rate, maximum (as a percent)	0.63%	1.39%	2.78%
Risk-free interest rate, minimum (as a percent)	0.59%	0.68%	1.22%
Dividend yield (as a percent)	5.00%	6.75%	6.75%
Volatility factors of the expected market price for our common stock, maximum (as a percent)	31.70%	42.90%	44.30%
Volatility factors of the expected market price for our common stock, minimum (as a percent)	24.20%	35.90%	35.70%
Weighted average expected life of options, maximum (in years)	4 years 2 months 1 day
Stock Option, Shares
Outstanding at the beginning of the period (in shares)	1,909,999
Granted (in shares)	512,706
Options exercised (in shares)	(149,340)
Options cancelled (in shares)	(14,602)
Outstanding at the end of the period (in shares)	2,258,763	1,909,999
Exercisable at the end of the period (in shares)	1,724,083
Stock Option, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 47.20
Options Granted (in dollars per share)	$ 67.36
Options exercised (in dollars per share)	$ 48.01
Options cancelled (in dollars per share)	$ 67.98
Outstanding at the end of the period (in dollars per share)	$ 51.59	$ 47.20
Exercisable at the end of the period (in dollars per share)	$ 47.65
Stock Option, Weighted Average Remaining Contractual Life (years)
Outstanding at the end of the period (in years)	6 years 7 months 6 days
Exercisable at the end of the period (in years)	5 years 10 months 24 days
Stock Option, Intrinsic Value
Outstanding at the end of the period	17,870,000
Exercisable at the end of the period	17,613,000
Nonvested Stock Options, Shares
Nonvested Options at the beginning of the period (in shares)	421,426
Granted (in shares)	512,706
Vested (in shares)	(384,844)
Cancelled (in shares)	(14,602)
Nonvested Options at the end of the period (in shares)	534,686	421,426
Nonvested Stock Options, Weighted Average Grant Date Fair Value
Nonvested stock options at the beginning of the period (in dollars per share)	$ 10.86
Granted (in dollars per share)	$ 9.25
Vested (in dollars per share)	$ 10.66
Cancelled (in dollars per share)	$ 7.88
Nonvested stock options at the end of the period (in dollars per share)	$ 9.54	$ 10.86
Stock Options | Minimum
Fair value assumptions of stock options using Black-Scholes option pricing model
Weighted average expected life of options, maximum (in years)		4 years 3 months	4 years 3 months
Stock Option, Range of Exercise Prices
Exercise Price Range, Number of Outstanding Options (in dollars per share)	$ 21.57	$ 21.57
Exercise price range, options granted (in dollars per share)	$ 65.93
Exercise Price Range, Options Exercised (in dollars per share)	$ 22.15
Exercise price range, options cancelled (in dollars per share)	$ 55.39
Exercise price range, options excercisable (in dollars per share)	$ 21.57
Stock Options | Maximum
Fair value assumptions of stock options using Black-Scholes option pricing model
Weighted average expected life of options, maximum (in years)		7 years	7 years
Stock Option, Range of Exercise Prices
Exercise Price Range, Number of Outstanding Options (in dollars per share)	$ 73.20	$ 57.19
Exercise price range, options granted (in dollars per share)	$ 73.20
Exercise Price Range, Options Exercised (in dollars per share)	$ 57.49
Exercise price range, options cancelled (in dollars per share)	$ 70.34
Exercise price range, options excercisable (in dollars per share)	$ 65.93
Stock Options | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	4,500,000	4,400,000	4,200,000
Restricted Stock or Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested awards	14,200,000
Weighted average period over which cost is recognized (in years)	2 years
Restricted Stock or Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	2 years
Restricted Stock or Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	5 years
Restricted Stock or Restricted Stock Units | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 16,100,000	$ 16,400,000	$ 15,100,000
Restricted Stock
Nonvested Restricted Stock and Restricted Stock Units, Shares
Nonvested at the beginning of the period (in shares)	591,884
Granted (in shares)	189,659
Vested (in shares)	(247,411)
Forfeited (in shares)	(25,016)
Nonvested at the end of the period (in shares)	509,116
Nonvested Restricted Stock and Restricted Stock Units, Weighted Average Grant Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 52.66
Granted (in dollars per share)	$ 67.05
Vested (in dollars per share)	$ 55.09
Forfeited (in dollars per share)	$ 56.31
Nonvested at the end of the period (in dollars per share)	$ 56.66
RestrictedStock Units
Nonvested Restricted Stock and Restricted Stock Units, Shares
Nonvested at the beginning of the period (in shares)	6,825
Granted (in shares)	4,635
Vested (in shares)	(3,592)
Forfeited (in shares)	(352)
Nonvested at the end of the period (in shares)	7,516
Nonvested Restricted Stock and Restricted Stock Units, Weighted Average Grant Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 50.34
Granted (in dollars per share)	$ 64.72
Vested (in dollars per share)	$ 46.68
Forfeited (in dollars per share)	$ 53.74
Nonvested at the end of the period (in dollars per share)	$ 60.80
Employee Stock Ownership Plan (ESOP), Plan [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance	2,500,000
Number of shares available for future issuance	2,436,733
Number of shares purchased	63,267
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount related to the Employee Stock Purchase Plan	90.00%
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount related to the Employee Stock Purchase Plan	95.00%
2012 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance		8,836,614
Number of shares available for future issuance	8,169,232