Stock-Based Compensation Plans (Details 3) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2014 item	Sep. 09, 2014	Oct. 31, 1996
Additional disclosures
Baseline share value (in dollars per share)					$ 155.83
Stock-based compensation expense	$ 13,314	$ 17,775	$ 9,961
Capitalized stock-based compensation cost	5,457	8,379	5,140
Forfeiture rate (as a percent)	1.40%
Employee Stock Purchase Plan [Abstract]
Shares issued under Employee Stock Purchase Plan	9,848
Stock-based compensation expense	13,314	17,775	9,961
Stock Options
Weighted average assumptions
Weighted average fair value per share (in dollars per share)		$ 26.78	$ 29.11
Life of options (in years)		5 years	5 years
Dividend yield (as a percent)		3.70%	3.50%
Volatility (as a percent)		34.00%	35.00%
Risk-free interest rate (as a percent)		0.91%	0.87%
Additional disclosures
Unrecognized compensation cost for unvested stock options	1,058
Weighted average period for recognition of unrecognized compensation cost	1 year 1 month 6 days
Forfeiture rate (as a percent)	1.40%
Restricted stock
Additional disclosures
Restricted stock granted (in shares)	98,954
Number of shares issued during period for new grants and conversion of units	115,163
Number of shares issued due to conversion of units	16,209
Number of shares issued due to new awards	98,954
Fair value of shares issued for new awards	12,799
Outstanding unvested shares granted	190,240	182,083
Number of shares vested during period related to new grants and conversion of units	99,036
Number of shares vested during period related to conversion of units	5,073
Number of shares vested during period related to new awards	93,963
Total fair value of shares vested	11,352	14,832	36,337
Unrecognized compensation cost for unvested stock options	19,559
Weighted average period for recognition of unrecognized compensation cost	3 years 7 months 6 days
Restricted stock | Minimum
Additional disclosures
Grant date fair value per share (in dollars per share)	$ 74.20
Restricted stock | Maximum
Additional disclosures
Grant date fair value per share (in dollars per share)	$ 163.39
Restricted stock units
Weighted average assumptions
Dividend yield (as a percent)	3.60%
Maximum Measurement Period (in years)	3 years
Award vesting period (in years)	3 years
Additional disclosures
Restricted stock granted (in shares)	131,980
Unrecognized compensation cost for unvested restricted stock	15,522
Restricted stock granted based on total shareholder metrics (in shares)	58,206
Restricted stock granted based on financial metrics (in shares)	73,774
Baseline share value (in dollars per share)	$ 128.97
Estimated volatility, Minimum (as a percent)	17.60%
Estimated volatility, Maximum (as a percent)	18.60%
Historical volatility (as a percent)	50.00%
Implied volatility (as a percent)	50.00%
Risk-free interest rate, minimum (as a percent)	0.04%
Risk-free interest rate, maximum (as a percent)	0.72%
Average estimated fair value (in dollars per share)	$ 103.20
Restricted stock units | Maximum
Weighted average assumptions
Percentage of stock based compensation elected to be received in the form of stock options upon the election of the recipient	25.00%
Non Qualified Employee Stock Purchase Plan [Member]
Additional disclosures
Stock-based compensation expense	407	174	127
Employee Stock Purchase Plan [Abstract]
Employee stock purchase plan, shares of common stock reserved for issuance						1,000,000
Employee stock purchase plan, remaining shares of common stock available for issuance	714,827
Employment period of full-time employees for becoming eligible to participate in the plan (in months)	1 month
Employment period of other employees for becoming eligible to participate in the plan (in months)	12 months
Purchase period (in months)		7 months		6 months
Number of purchase periods				2
Employee stock purchase plan, discounted stock price percentage	85.00%
Shares issued under Employee Stock Purchase Plan	9,848	9,260	6,260
Stock-based compensation expense	$ 407	$ 174	$ 127