Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 37,435	$ 65,885	$ 77,417
Adjustment to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	68,675	63,808	56,538
Amortization of contract acquisition costs	659	900	856
Amortization of debt issuance costs	753	712	705
Imputed interest expense and fair value adjustments to contingent consideration	(4,523)	716	(6,233)
Provision for doubtful accounts	1,164	1,465	633
Gain on disposal of assets	(44)	(166)	141
Impairment losses	32,050	8,100	373
Loss on assets held-for-sale	5,300	0	0
Deferred income taxes	(1,583)	9,317	9,514
Excess tax benefit from equity-based awards	(601)	(662)	(1,399)
Equity-based compensation expense	9,773	11,304	11,307
(Gain) loss on foreign currency derivatives	1,710	(1,469)	(1,548)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	(7,858)	(19,867)	(41,005)
Prepaids and other assets	(92)	(5,379)	(5,300)
Accounts payable and accrued expenses	(23,074)	11,941	(8,115)
Deferred revenue and other liabilities	(11,847)	(12,855)	206
Net cash provided by operating activities	107,897	133,750	94,090
Cash flows from investing activities
Proceeds from sale of long-live assets	114	202	135
Purchases of property, plant and equipment	(50,832)	(66,595)	(67,641)
Investments in non-marketable equity investments	(3,179)	(9,000)	0
Acquisitions, net of cash acquired of zero and zero, respectively	(46,460)	(1,776)	(24,416)
Net cash used in investing activities	(100,357)	(77,169)	(91,922)
Cash flows from financing activities
Proceeds from line of credit	2,093,500	2,262,350	2,077,400
Payments on line of credit	(1,976,200)	(2,262,350)	(2,077,400)
Payments on other debt	(3,222)	(3,222)	(4,504)
Payments of contingent consideration and hold back payments to acquisitions	(9,467)	(11,883)	(8,547)
Dividends paid to shareholders	(18,262)	(17,423)	0
Payments to noncontrolling interest	(4,317)	(4,593)	(5,962)
Purchase of mandatorily redeemable noncontrolling interest	(4,105)	0	0
Proceeds from exercise of stock options	371	825	443
Excess tax benefit from equity-based awards	601	662	1,399
Payments of debt issuance costs	(1,888)	(35)	0
Purchase of treasury stock	(74,683)	(17,231)	(57,074)
Net cash used in financing activities	2,328	(52,900)	(74,245)
Effect of exchange rate changes on cash and cash equivalents	(14,908)	(20,693)	(8,624)
Increase (decrease) in cash and cash equivalents	(5,040)	(17,012)	(80,701)
Cash and cash equivalents, beginning of period	60,304	77,316	158,017
Cash and cash equivalents, end of period	55,264	60,304	77,316
Supplemental disclosures
Cash paid for interest	6,976	6,052	5,404
Cash paid for income taxes	19,741	15,178	14,545
Non-cash investing and financing activities
Acquisition of long lived assets through capital leases	584	10,492	696
Acquisition of equipment through increase in accounts payable, net	681	(386)	(4,170)
Contract acquisition costs credited to accounts receivable	$ 206	$ 1,055	$ 471