Stock-Based Compensation Plans (Details)	3 Months Ended
	Mar. 31, 2017 $ / shares shares
Shares
Exercised (in shares)	(7,266)
2009 Plan | Employee and Directors Stock Options [Member]
Shares
Options outstanding at the beginning of the period (in shares)	177,333
Exercised (in shares)	(3,085)
Forfeited (in shares)	0
Options outstanding at the end of the period (in shares)	174,248
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 124.25
Exercised (in dollars per share) | $ / shares	120.74
Forfeited (in dollars per share) | $ / shares	0.00
Options outstanding at the end of the period (in dollars per share) | $ / shares	$ 124.31
1994 Plan | Employee and Directors Stock Options [Member]
Shares
Options outstanding at the beginning of the period (in shares)	22,541
Exercised (in shares)	(4,181)
Forfeited (in shares)	0
Options outstanding at the end of the period (in shares)	18,360
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 77.91
Exercised (in dollars per share) | $ / shares	129.72
Forfeited (in dollars per share) | $ / shares	0.00
Options outstanding at the end of the period (in dollars per share) | $ / shares	$ 66.11