Acquisitions (Narrative) (Details) $ in Thousands			12 Months Ended
	Dec. 31, 2015 USD ($) employee shares	Feb. 23, 2015 USD ($) employee	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) entity	Dec. 31, 2015 USD ($) shares
Business Acquisition [Line Items]
Deferred contingent consideration liability, non-current			$ 1,972	$ 943
Deferred contingent consideration liability	$ 8,782		3,870	1,723	$ 8,782
Purchase price allocation of goodwill			637,287	625,027
Deferred contingent consideration liability, current			3,897	10,780
Payments of contingent acquisition liabilities			10,330	828	4,592
Uncertain tax positions	1,300		6,900		1,300
Energy [Member]
Business Acquisition [Line Items]
Purchase price allocation of goodwill			80,109	77,924
Healthcare [Member]
Business Acquisition [Line Items]
Purchase price allocation of goodwill			278,130	$ 272,032
Other Acquisitions [Member]
Business Acquisition [Line Items]
Number of businesses acquired | entity				3
Purchase price				$ 19,100
Cash paid for acquisition				$ 17,600
Payments of contingent acquisition liabilities			330
Other Acquisitions [Member] | Energy [Member]
Business Acquisition [Line Items]
Number of businesses acquired | entity				1
Other Acquisitions [Member] | Healthcare [Member]
Business Acquisition [Line Items]
Number of businesses acquired | entity				2
McKinnis Consulting Services, LLC [Member] | Healthcare [Member]
Business Acquisition [Line Items]
Purchase price	45,700
Cash paid for acquisition	$ 42,700
Date of acquisition	Dec. 31, 2015
Number of professionals in acquired entity | employee	70
Common stock issued to acquiree	$ 3,000				$ 3,000
Common stock issued to acquiree, shares | shares	176,758				176,758
Contingent consideration, maximum target	$ 10,000				$ 10,000
Contingent consideration, target period	1 year
Deferred contingent consideration liability, non-current	$ 8,300				8,300
Deferred contingent consideration liability	10,000				10,000
Payment to the selling members for undistributed cash held in the business as of the closing				$ 5,500
Purchase price allocation of identifiable intangible assets	13,000				13,000
Purchase price allocation of goodwill	45,500				45,500
Purchase price allocation of other net assets	$ 1,000				$ 1,000
Payments of contingent acquisition liabilities			$ 10,000
RevenueMed, Inc [Member] | Healthcare [Member]
Business Acquisition [Line Items]
Cash paid for acquisition		$ 21,300
Date of acquisition		Feb. 23, 2015
Number of professionals in acquired entity | employee		1,500
Contingent consideration, maximum target		$ 4,000
Contingent consideration, target period		6 months
Purchase price allocation of identifiable intangible assets		$ 7,300
Purchase price allocation of goodwill		14,400
Purchase price allocation of other net assets		2,600
Deferred contingent consideration liability, current		3,800
Payments of contingent acquisition liabilities		4,000
Purchase price allocation of internally developed software		1,400
Uncertain tax positions		$ 1,300