Stock-Based Compensation Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-Based Compensation Plans
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Shares
Exercised (in shares)	(500,197)
Granted (in shares)		215,230	115,303
2009 Plan
Stock-Based Compensation Plans
Common stock, par value (in dollars per share)	$ 0.01
Common stock shares available for grant	1,673,193
2009 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	501,568	307,554	247,403
Exercised (in shares)	(157,454)	(19,949)	(43,265)
Granted (in shares)	0	215,230	115,303
Forfeited (in shares)	(4,052)	(1,267)	(11,887)
Options outstanding at the end of the period (in shares)	340,062	501,568	307,554
Options exercisable at the end of the period (in shares)	185,227	184,167	74,618
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 120.77	$ 112.67	98.42
Exercised (in dollars per share)	$ 116.40	$ 84.43	85.09
Granted (in dollars per share)	$ 0.00	$ 129.03	133.16
Forfeited (in dollars per share)	$ 131.05	$ 131.56	115.15
Options outstanding at the end of the period (in dollars per share)	$ 122.67	$ 120.77	112.67
Options exercisable at the end of the period (in dollars per share)	$ 116.71	$ 107.18	97.46
1994 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	691,526	719,830	1,112,959
Exercised (in shares)	(342,743)	(24,292)	(364,519)
Granted (in shares)	0	0	0
Forfeited (in shares)	(76,381)	(4,012)	(28,610)
Options outstanding at the end of the period (in shares)	272,402	691,526	719,830
Options exercisable at the end of the period (in shares)	272,402	691,526	719,830
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 106.19	$ 105.40	94.10
Exercised (in dollars per share)	$ 99.03	$ 79.42	68.21
Granted (in dollars per share)	$ 0.00	$ 0.00	0.00
Forfeited (in dollars per share)	$ 142.66	$ 127.56	139.58
Options outstanding at the end of the period (in dollars per share)	$ 104.96	$ 106.19	105.40
Options exercisable at the end of the period (in dollars per share)	$ 104.96	$ 106.19	105.40