Stock-Based Compensation - Options outstanding (Details) - Stock options	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Options Outstanding
Number Outstanding (in shares) | shares	130,483
Weighted Average Remaining Contractual Life	6 years 8 months 19 days
Weighted Average Exercise Price (in dollars per share)	$ 54.46
Options Exercisable
Number Exercisable (in shares) | shares	82,056
Weighted Average Exercise Price (in dollars per share)	$ 53.38
$29.05–$37.41
Information about options outstanding
Low end of exercise price range (in dollars per share)	29.05
High end of exercise price range (in dollars per share)	$ 37.41
Options Outstanding
Number Outstanding (in shares) | shares	11,300
Weighted Average Remaining Contractual Life	5 years 3 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 35.01
Options Exercisable
Number Exercisable (in shares) | shares	11,300
Weighted Average Exercise Price (in dollars per share)	$ 35.01
$54.76–$54.76
Information about options outstanding
Low end of exercise price range (in dollars per share)	54.76
High end of exercise price range (in dollars per share)	$ 54.76
Options Outstanding
Number Outstanding (in shares) | shares	57,769
Weighted Average Remaining Contractual Life	6 years 5 months 16 days
Weighted Average Exercise Price (in dollars per share)	$ 54.76
Options Exercisable
Number Exercisable (in shares) | shares	34,020
Weighted Average Exercise Price (in dollars per share)	$ 54.76
$57.47–$60.10
Information about options outstanding
Low end of exercise price range (in dollars per share)	57.47
High end of exercise price range (in dollars per share)	$ 60.10
Options Outstanding
Number Outstanding (in shares) | shares	61,414
Weighted Average Remaining Contractual Life	7 years 2 months 19 days
Weighted Average Exercise Price (in dollars per share)	$ 57.76
Options Exercisable
Number Exercisable (in shares) | shares	36,736
Weighted Average Exercise Price (in dollars per share)	$ 57.75