Business Combinations and Goodwill (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 companies	Dec. 31, 2012 companies
Business Combinations
Number of companies acquired	3	2
Total consideration transferred for businesses acquired	$ 16,200,000	$ 10,900,000
Purchase Price Allocation
Amount of purchase price allocated to goodwill	12,342,000	8,749,000
Amount of purchase price allocated to acquired intangible assets	5,100,000	2,300,000
Amount of purchase price allocated to other net liabilities assumed	1,200,000	100,000
Goodwill Roll Forward
Goodwill, beginning balance	68,742,000	59,993,000
Acquisitions	12,342,000	8,749,000
Goodwill, ending balance	81,084,000	68,742,000
Companies Acquired in Current Period
Business Combinations
Weighted-average useful life of finite-lived intangible assets acquired as part of acquisitions	3 years 2 months
Goodwill
Goodwill deductible for tax purposes	0
Companies Acquired in Previous Periods
Business Combinations
Payments made during period related to previous acquisitions	1,500,000
Fair value of remaining liability to former owners of acquirees at year-end	$ 500,000