Stock-Based Compensation Plans (Details 6) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted stock
Restricted stock shares
Outstanding at the beginning of the period (in shares)	179,307	182,083	202,218
Granted (in shares)	61,953	98,954	123,977
Vested (in shares)	(91,847)	(93,963)	(141,673)
Forfeited (in shares)	(1,529)	(7,767)	(2,439)
Outstanding at the ending of the period (in shares)	147,884	179,307	182,083
Restricted stock shares weighted average grant date fair value per share
Outstanding at the beginning of the period (in dollars per share)	$ 129.06	$ 124.35	$ 107.58
Granted (in dollars per share)	173.04	129.35	129.21
Vested (in dollars per share)	130.75	120.81	104.69
Forfeited (in dollars per share)	151.86	128.62	123.05
Outstanding at the ending of the period (in dollars per share)	$ 146.21	$ 129.06	$ 124.35
Restricted stock converted from performance shares
Restricted stock shares
Outstanding at the beginning of the period (in shares)	10,933	0	0
Granted (in shares)	95,826	16,209
Vested (in shares)	(8,412)	(5,073)
Forfeited (in shares)	0	(203)
Outstanding at the ending of the period (in shares)	98,347	10,933	0