Stock-Based Compensation Plans (Details 4) - Performance awards - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Performance awards
Outstanding at the beginning of the period (in shares)	238,266	239,902	189,765
Granted (in shares)	94,054	85,636	136,276
Increase (decrease) in awards based on performance (in shares)	36,091	14,697	(46,790)
Converted to restricted stock (in shares)	(115,618)	(95,826)	(16,209)
Forfeited (in shares)	(1,630)	(6,143)	(23,140)
Outstanding at the ending of the period (in shares)	251,163	238,266	239,902
Weighted average grant date fair value per award
Outstanding at the beginning of the period (in dollars per share)	$ 119.65	$ 95.20	$ 70.00
Granted (in dollars per share)	141.92	148.49	117.43
Change in awards based on performance (in dollars per share)	101.52	78.50	74.37
Converted to restricted stock (in dollars per share)	94.67	78.50	74.37
Forfeited (in dollars per share)	141.98	110.34	76.22
Outstanding at the ending of the period (in dollars per share)	$ 136.74	$ 119.65	$ 95.20
Grants in period based on shareholder metrics (in shares)	61,039	55,162	60,391
Grants in period based on financial metrics (in shares)	33,015	30,474	75,885