Stock-Based Compensation Plans (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-Based Compensation Plans
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Shares
Exercised (in shares)	(131,499)
2009 Plan
Stock-Based Compensation Plans
Common stock, par value (in dollars per share)	$ 0.01
Common stock shares available for grant	878,622
2009 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	249,178	340,062	501,568
Exercised (in shares)	(71,845)	(90,884)	(157,454)
Granted (in shares)	0	0	0
Forfeited (in shares)	0	0	(4,052)
Options outstanding at the end of the period (in shares)	177,333	249,178	340,062
Options exercisable at the end of the period (in shares)	177,333	188,081	185,227
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 122.17	$ 122.67	$ 120.77
Exercised (in dollars per share)	117.04	124.01	116.40
Granted (in dollars per share)	0.00	0.00	0.00
Forfeited (in dollars per share)	0.00	0.00	131.05
Options outstanding at the end of the period (in dollars per share)	124.25	122.17	122.67
Options exercisable at the end of the period (in dollars per share)	$ 124.25	$ 119.98	$ 116.71
1994 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	82,195	272,402	691,526
Exercised (in shares)	(59,654)	(190,207)	(342,743)
Granted (in shares)	0	0	0
Forfeited (in shares)	0	0	(76,381)
Options outstanding at the end of the period (in shares)	22,541	82,195	272,402
Options exercisable at the end of the period (in shares)	22,541	82,195	272,402
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share)	$ 103.27	$ 104.96	$ 106.19
Exercised (in dollars per share)	112.85	105.70	99.03
Granted (in dollars per share)	0.00	0.00	0.00
Forfeited (in dollars per share)	0.00	0.00	142.66
Options outstanding at the end of the period (in dollars per share)	77.91	103.27	104.96
Options exercisable at the end of the period (in dollars per share)	$ 77.91	$ 103.27	$ 104.96