Share-Based Compensation - Information pertaining to options oustanding - (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation
Range of exercise prices, low end of range (in dollars per share)	$ 61.42	$ 61.42	$ 61.49
Range of exercise prices, high end of range (in dollars per share)	$ 69.48	$ 66.32	$ 66.32
Options Outstanding
Number outstanding (in shares)	246,535
Weighted Average Remaining Contractual Life	4 years 9 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 42.53
Options Exercisable
Number outstanding (in shares)	185,758
Weighted Average Exercise Price (in dollars per share)	$ 36.33
Weighted Average Remaining Contractual Life	3 years 9 months 18 days
Restricted Stock.
Vesting schedule of shares
2016	58,992
2017	35,620
2018	31,167
2019	39,033
2020	3,405
Thereafter	14,797
Total	183,014	218,282
$26.01 - $ 30.00
Share Based Compensation
Range of exercise prices, low end of range (in dollars per share)	$ 26.01
Range of exercise prices, high end of range (in dollars per share)	$ 30.00
Options Outstanding
Number outstanding (in shares)	24,296
Weighted Average Remaining Contractual Life	2 years 3 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 27.46
Options Exercisable
Number outstanding (in shares)	24,296
Weighted Average Exercise Price (in dollars per share)	$ 27.46
$30.01 - $35.00
Share Based Compensation
Range of exercise prices, low end of range (in dollars per share)	30.01
Range of exercise prices, high end of range (in dollars per share)	$ 35.00
Options Outstanding
Number outstanding (in shares)	93,388
Weighted Average Remaining Contractual Life	3 years 4 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 31.69
Options Exercisable
Number outstanding (in shares)	93,385
Weighted Average Exercise Price (in dollars per share)	$ 31.69
$35.01 - $40.00
Share Based Compensation
Range of exercise prices, low end of range (in dollars per share)	35.01
Range of exercise prices, high end of range (in dollars per share)	$ 40.00
Options Outstanding
Number outstanding (in shares)	29,735
Weighted Average Remaining Contractual Life	2 years 2 months 12 days
Weighted Average Exercise Price (in dollars per share)	$ 36.90
Options Exercisable
Number outstanding (in shares)	29,732
Weighted Average Exercise Price (in dollars per share)	$ 36.89
$40.01 - $45.00
Share Based Compensation
Range of exercise prices, low end of range (in dollars per share)	40.01
Range of exercise prices, high end of range (in dollars per share)	$ 45.00
Options Outstanding
Number outstanding (in shares)	24,507
Weighted Average Remaining Contractual Life	5 years 10 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 41.42
Options Exercisable
Number outstanding (in shares)	19,163
Weighted Average Exercise Price (in dollars per share)	$ 41.41
$45.01 - $69.48
Share Based Compensation
Range of exercise prices, low end of range (in dollars per share)	45.01
Range of exercise prices, high end of range (in dollars per share)	$ 88.05
Options Outstanding
Number outstanding (in shares)	74,609
Weighted Average Remaining Contractual Life	8 years 1 month 6 days
Weighted Average Exercise Price (in dollars per share)	$ 63.61
Options Exercisable
Number outstanding (in shares)	19,182
Weighted Average Exercise Price (in dollars per share)	$ 64.25