Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 68,597	$ 57,791	$ 37,260
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	44,515	46,255	43,094
Amortization of intangibles	14,170	14,396	14,863
Amortization of deferred grants	(973)	(1,348)	(1,148)
Unrealized foreign currency transaction (gains) losses, net	318	119	6,302
Stock-based compensation expense	8,749	6,381	4,873
Excess tax (benefit) from stock-based compensation	(422)
Deferred income tax provision (benefit)	2,515	4,865	(362)
Net (gain) loss on disposal of property and equipment	381	(2,030)	201
Bad debt expense (reversals)	278	(181)	483
Write-downs (recoveries) of value added tax receivables		(638)	143
Unrealized (gains) losses on financial instruments, net	1,028	2,352	(15)
Foreign exchange (gain) loss on liquidation of foreign entities	720	113	(83)
Amortization of deferred loan fees	403	259	259
Net (gain) on insurance settlement	(919)
Proceeds from business interruption insurance settlement	156
Imputed interest expense and fair value adjustments to contingent consideration	408
Other	(106)	(10)	(116)
Changes in assets and liabilities, net of acquisition:
Receivables	2,499	(40,276)	(22,062)
Prepaid expenses	(3,040)	336	(3,931)
Other current assets	(6,972)	(6,673)	(1,177)
Deferred charges and other assets	1,951	3,545	(2,754)
Accounts payable	(124)	2,029	(1,282)
Income taxes receivable / payable	(5,666)	2,609	804
Accrued employee compensation and benefits	(1,481)	5,179	9,140
Other accrued expenses and current liabilities	(1,564)	(5,026)	(2,025)
Deferred revenue	(2,559)	2,147	2,826
Other long-term liabilities	(2,398)	2,070	925
Net cash provided by operating activities	120,464	94,264	86,218
Cash flows from investing activities:
Capital expenditures	(49,662)	(44,683)	(59,193)
Cash paid for business acquisition, net of cash acquired	(9,370)
Proceeds from sale of property and equipment	616	3,639	388
Investment in restricted cash	(45)	(7)	(562)
Release of restricted cash	13	160
Proceeds from property and equipment insurance settlement	1,490
Net cash (used for) investing activities	(56,958)	(40,891)	(59,367)
Cash flows from financing activities:
Payments of long-term debt	(10,000)	(23,000)	(25,000)
Proceeds from issuance of long-term debt	5,000		32,000
Proceeds from issuance of common stock			59
Excess tax benefit from stock-based compensation	422
Cash paid for repurchase of common stock	(20,879)	(12,581)	(5,479)
Proceeds from grants	670	256	201
Payments on short-term debt	(323)
Shares repurchased for minimum tax withholding on equity awards	(3,326)	(437)	(227)
Cash paid for loan fees related to long-term debt	(962)
Net cash provided by (used for) financing activities	(29,398)	(35,762)	1,554
Effects of exchange rates on cash and cash equivalents	(13,887)	(14,459)	(3,742)
Net increase (decrease) in cash and cash equivalents	20,221	3,152	24,663
Cash and cash equivalents - beginning	215,137	211,985	187,322
Cash and cash equivalents - ending	235,358	215,137	211,985
Supplemental disclosures of cash flow information:
Cash paid during period for interest	1,476	1,716	2,149
Cash paid during period for income taxes	30,467	16,560	16,889
Non-cash transactions:
Property and equipment additions in accounts payable	4,941	5,512	6,002
Unrealized gain (loss) on postretirement obligation in accumulated other comprehensive income (loss)	$ (75)	$ 28	$ (181)