Stock-Based Compensation Plans (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-Based Compensation Plans
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Shares
Exercised (in shares)	(281,091)
Granted (in shares)			215,230
2009 Plan
Stock-Based Compensation Plans
Common stock, par value (in dollars per share)	$ 0.01
Common stock shares available for grant	1,364,678
2009 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	340,062	501,568	307,554
Exercised (in shares)	(90,884)	(157,454)	(19,949)
Granted (in shares)	0	0	215,230
Forfeited (in shares)	0	(4,052)	(1,267)
Options outstanding at the end of the period (in shares)	249,178	340,062	501,568
Options exercisable at the end of the period (in shares)	188,081	185,227	184,167
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 122.67	$ 120.77	$ 112.67
Exercised (in dollars per share)	124.01	116.40	84.43
Granted (in dollars per share)	0.00	0.00	129.03
Forfeited (in dollars per share)	0.00	131.05	131.56
Options outstanding at the end of the period (in dollars per share)	122.17	122.67	120.77
Options exercisable at the end of the period (in dollars per share)	$ 119.98	$ 116.71	$ 107.18
1994 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	272,402	691,526	719,830
Exercised (in shares)	(190,207)	(342,743)	(24,292)
Granted (in shares)	0	0	0
Forfeited (in shares)	0	(76,381)	(4,012)
Options outstanding at the end of the period (in shares)	82,195	272,402	691,526
Options exercisable at the end of the period (in shares)	82,195	272,402	691,526
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 104.96	$ 106.19	$ 105.40
Exercised (in dollars per share)	105.70	99.03	79.42
Granted (in dollars per share)	0.00	0.00	0.00
Forfeited (in dollars per share)	0.00	142.66	127.56
Options outstanding at the end of the period (in dollars per share)	103.27	104.96	106.19
Options exercisable at the end of the period (in dollars per share)	$ 103.27	$ 104.96	$ 106.19