The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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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	$ 441,023,000us-gaap_SalesRevenueServicesNet	$ 442,443,000us-gaap_SalesRevenueServicesNet	$ 434,424,000us-gaap_SalesRevenueServicesNet	$ 406,851,000us-gaap_SalesRevenueServicesNet	$ 396,070,000us-gaap_SalesRevenueServicesNet	$ 394,400,000us-gaap_SalesRevenueServicesNet	$ 380,779,000us-gaap_SalesRevenueServicesNet	$ 351,852,000us-gaap_SalesRevenueServicesNet	$ 1,724,741,000us-gaap_SalesRevenueServicesNet	$ 1,523,101,000us-gaap_SalesRevenueServicesNet	$ 1,031,935,000us-gaap_SalesRevenueServicesNet
Gross profit	142,537,000us-gaap_GrossProfit	144,838,000us-gaap_GrossProfit	141,905,000us-gaap_GrossProfit	128,155,000us-gaap_GrossProfit	120,985,000us-gaap_GrossProfit	119,016,000us-gaap_GrossProfit	113,105,000us-gaap_GrossProfit	101,769,000us-gaap_GrossProfit	557,435,000us-gaap_GrossProfit	454,875,000us-gaap_GrossProfit	321,254,000us-gaap_GrossProfit
Operating Income									137,782,000us-gaap_OperatingIncomeLoss	116,587,000us-gaap_OperatingIncomeLoss	73,013,000us-gaap_OperatingIncomeLoss
Depreciation									12,300,000us-gaap_Depreciation	7,200,000us-gaap_Depreciation	5,700,000us-gaap_Depreciation
Amortization of intangible assets									22,130,000us-gaap_AmortizationOfIntangibleAssets	20,943,000us-gaap_AmortizationOfIntangibleAssets	17,047,000us-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)									3us-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
Life Sciences Europe [Member]
Segment Reporting Information
Revenues									41,369,000	39,438,000	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									(53,745,000)	(48,119,000)	(46,362,000)
Amortization of intangible assets									$ 9,000	$ 90,000	$ 291,000