Stock-Based Compensation Plans (Details)	3 Months Ended
	Mar. 31, 2016 $ / shares shares
Shares
Exercised (in shares)	(14,530)
2009 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	249,178
Exercised (in shares)	(6,660)
Forfeited (in shares)	0
Options outstanding at the end of the period (in shares)	242,518
Options exercisable at the end of the period (in shares)	242,518
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 122.17
Exercised (in dollars per share) | $ / shares	126.99
Forfeited (in dollars per share) | $ / shares	0.00
Options outstanding at the end of the period (in dollars per share) | $ / shares	122.04
Options exercisable at the end of the period (in dollars per share) | $ / shares	$ 122.04
1994 Plan | Stock Options
Shares
Options outstanding at the beginning of the period (in shares)	82,195
Exercised (in shares)	(7,870)
Forfeited (in shares)	0
Options outstanding at the end of the period (in shares)	74,325
Options exercisable at the end of the period (in shares)	74,325
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 103.27
Exercised (in dollars per share) | $ / shares	100.36
Forfeited (in dollars per share) | $ / shares	0.00
Options outstanding at the end of the period (in dollars per share) | $ / shares	103.57
Options exercisable at the end of the period (in dollars per share) | $ / shares	$ 103.57