Earnings Per Common Share - Calculation of diluted EPS under Treasury method - (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share
Number of shares	72,480	46,798	72,480	47,865
Range of exercise prices, low end of range (in dollars per share)			$ 61.42	$ 61.42
Range of exercise prices, high end of range (in dollars per share)	$ 69.48	$ 66.32	$ 69.48	$ 66.32