Stock-based Compensation - Weighted Average Valuation Assumptions (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend Yield	0.40%	0.40%	0.30%
Expected Volatility	32.80%	34.20%	28.90%
Risk-free Interest Rate	1.90%	1.30%	1.60%
Expected Term (in years)	5 years 3 months 12 days	5 years 3 months 12 days	5 years 2 months 12 days
Weighted-average Fair Value of Stock Options Granted (in dollars per share)	$ 8.55	$ 7.10	$ 8.41