Stock-Based Compensation - Summary of Restricted Stock, Stock Grants, Stock Units and Performance Shares (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Units, Stock Grants, and Stock Units
Stocks granted and the weighted average fair value
Units granted (in shares)	161,963	141,811	152,651
Grant date fair value (in dollars per share)	$ 72.60	$ 67.34	$ 64.12
Number of granted awards to be settled in cash (in shares)	67,599	43,952	45,104
Performance Shares
Stocks granted and the weighted average fair value
Units granted (in shares)	147,706	166,666	151,430
Grant date fair value (in dollars per share)	$ 78.99	$ 66.60	$ 64.97