Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities
Net income	$ 77,417	$ 71,471	$ 73,923
Adjustment to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	56,538	46,064	41,166
Amortization of contract acquisition costs	856	1,160	1,017
Amortization of debt issuance costs	705	659	808
Imputed interest expense and fair value adjustments to contingent consideration	(6,233)	3,301	904
Provision for doubtful accounts	633	695	368
Loss (gain) on disposal of assets	141	0	305
Impairment losses	373	1,205	2,958
Deferred income taxes	9,514	6,892	2,354
Excess tax benefit from equity-based awards	(1,399)	(1,343)	(462)
Equity-based compensation expense	11,307	13,234	13,376
Loss on foreign currency derivatives	(1,548)	234	414
Loss on deconsolidation of subsidiary, net of cash of zero, $897, and zero, respectively	0	2,758	0
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	(41,005)	7,291	400
Prepaids and other assets	(5,300)	(5,374)	(25,664)
Accounts payable and accrued expenses	(8,115)	(2,549)	(16,301)
Deferred revenue and other liabilities	206	(7,718)	11,354
Net cash provided by operating activities	94,090	137,979	106,920
Cash flows from investing activities
Proceeds from grant for property, plant and equipment	0	0	110
Proceeds from sale of long-lived assets	135	0	450
Purchases of property, plant and equipment, net of acquisitions	(67,641)	(50,364)	(40,653)
Acquisitions, net of cash acquired of $3,525, $6,423, and $3,744, respectively	(24,416)	(9,166)	(40,839)
Net cash used in investing activities	(91,922)	(59,530)	(80,932)
Cash flows from financing activities
Proceeds from line of credit	2,077,400	1,533,550	1,179,850
Payments on line of credit	(2,077,400)	(1,541,550)	(1,135,850)
Proceeds from other debt		3,709	8,014
Payments on other debt	(4,504)	(5,789)	(4,900)
Payment of contingent consideration related to acquisitions	(8,547)
Dividends paid to noncontrolling interest	(5,962)	(4,455)	(2,205)
Proceeds from exercise of stock options	443	862	1,374
Excess tax benefit from equity-based awards	1,399	1,343	462
Purchase of treasury stock	(57,074)	(56,532)	(81,243)
Payments of debt issuance costs	0	(1,800)	(467)
Net cash used in financing activities	(74,245)	(70,662)	(34,965)
Effect of exchange rate changes on cash and cash equivalents	(8,624)	(14,255)	17,091
(Decrease) increase in cash and cash equivalents	(80,701)	(6,468)	8,114
Cash and cash equivalents, beginning of period	158,017	164,485	156,371
Cash and cash equivalents, end of period	77,316	158,017	164,485
Supplemental disclosures
Cash paid for interest	5,404	4,220	4,412
Cash paid for income taxes	14,545	16,757	16,388
Non-cash investing and financing activities
Purchases of equipment through financing arrangements	696	0	6,100
Acquisition of equipment through increse in accounts payable	4,170	2,762	0
Landlord incentives credited to deferred rent	0	1,016	1,723
Contract acquisition costs credited to accounts receivable	$ 471	$ 1,000	$ 0