Business Acquisitions - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired	$ 172,200,000	$ 126,800,000
Goodwill recognized through acquisitions	64,700,000
R.W. Lyall & Company, Inc.
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired	129,200,000
Intangible assets	69,600,000
Goodwill recognized through acquisitions	$ 47,700,000
Weighted average useful life	21 years
EMC
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired	$ 43,000,000
Intangible assets	16,500,000
Goodwill recognized through acquisitions	$ 17,000,000
Weighted average useful life	19 years
Goodwill, expected to be tax deductible	$ 0