Employee Benefit Plans - Weighted Average Assumptions on Option Pricing (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee benefit plans [Line Items]
Document Fiscal Year Focus	2017
Performance Restricted Stock Units [Member]
Employee benefit plans [Line Items]
Dividend yield (as a percent)	1.37%	2.12%	1.90%
Expected volatility (as a percent)	25.19%	30.84%	32.20%
Risk free interest rate (as a percent)	1.48%	0.90%	0.82%
Weighted average grant date fair value (in dollars per share)	$ 53.74	$ 25.62	$ 28.31