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Business Segments (Segment Reporting Information) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 segment	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information
Revenues	$ 475,808,000us-gaap_SalesRevenueServicesNet	$ 477,391,000us-gaap_SalesRevenueServicesNet	$ 468,081,000us-gaap_SalesRevenueServicesNet	$ 438,642,000us-gaap_SalesRevenueServicesNet	$ 422,906,000us-gaap_SalesRevenueServicesNet	$ 420,623,000us-gaap_SalesRevenueServicesNet	$ 407,244,000us-gaap_SalesRevenueServicesNet	$ 378,154,000us-gaap_SalesRevenueServicesNet	$ 1,859,922,000us-gaap_SalesRevenueServicesNet	$ 1,628,927,000us-gaap_SalesRevenueServicesNet	$ 1,134,614,000us-gaap_SalesRevenueServicesNet
Gross profit	153,534,000us-gaap_GrossProfit	155,182,000us-gaap_GrossProfit	152,203,000us-gaap_GrossProfit	136,993,000us-gaap_GrossProfit	129,094,000us-gaap_GrossProfit	126,398,000us-gaap_GrossProfit	120,745,000us-gaap_GrossProfit	109,252,000us-gaap_GrossProfit	597,912,000us-gaap_GrossProfit	485,489,000us-gaap_GrossProfit	352,709,000us-gaap_GrossProfit
Operating Income									146,270,000us-gaap_OperatingIncomeLoss	124,380,000us-gaap_OperatingIncomeLoss	82,272,000us-gaap_OperatingIncomeLoss
Depreciation									13,300,000us-gaap_Depreciation	8,000,000us-gaap_Depreciation	6,500,000us-gaap_Depreciation
Amortization of intangible assets									24,401,000us-gaap_AmortizationOfIntangibleAssets	21,686,000us-gaap_AmortizationOfIntangibleAssets	17,863,000us-gaap_AmortizationOfIntangibleAssets
Assets	1,274,174,000us-gaap_Assets				1,258,809,000us-gaap_Assets				1,274,174,000us-gaap_Assets	1,258,809,000us-gaap_Assets
Reportable segments (in number of segments)									4us-gaap_NumberOfReportableSegments
Apex
Segment Reporting Information
Revenues									1,190,052,000	1,059,993,000	617,844,000
Gross profit									335,322,000	294,611,000	174,968,000
Operating Income									121,334,000	98,588,000	57,191,000
Amortization of intangible assets									16,356,000	19,524,000	15,665,000
Oxford
Segment Reporting Information
Revenues									493,320,000	423,670,000	375,196,000
Gross profit									208,607,000	147,348,000	132,034,000
Operating Income									66,315,000	60,544,000	57,703,000
Amortization of intangible assets									5,491,000	965,000	437,000
Physician
Segment Reporting Information
Revenues									135,181,000	105,827,000	102,679,000
Gross profit									40,477,000	30,614,000	31,455,000
Operating Income									9,797,000	8,853,000	9,998,000
Amortization of intangible assets									2,272,000	742,000	816,000
Life Sciences Europe [Member]
Segment Reporting Information
Revenues									41,369,000	39,437,000	38,895,000
Gross profit									13,506,000	12,916,000	14,252,000
Operating Income									3,878,000	5,574,000	4,481,000
Amortization of intangible assets									274,000	364,000	654,000
Corporate
Segment Reporting Information
Operating Income									(55,054,000)	(49,179,000)	(47,101,000)
Amortization of intangible assets									$ 8,000	$ 91,000	$ 291,000