Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 56,432	$ 64,081	$ 48,926
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	51,629	52,149	57,817
Amortization of intangibles	14,003	16,639	15,542
Amortization of deferred grants	(1,119)	(351)	(657)
Impairment losses	41,553	1,711	9,401
Unrealized foreign currency transaction (gains) losses, net	2,123	(2,304)	(843)
Stock-based compensation expense	10,748	7,396	7,543
Deferred income tax provision (benefit)	(5,649)	282	(1,509)
Net (gain) loss on disposal of property and equipment	(158)	383	312
Unrealized (gains) losses and premiums on financial instruments, net	1,108	(1,059)	805
Net (gain) on insurance settlement		(1,133)
(Earnings) losses from equity method investees	1,099	448	639
(Gain) on dilution of investment in equity method investees	(1,357)
Other	1,615	785	464
Changes in assets and liabilities, net of acquisitions:
Receivables, net	(9,306)	(40,239)	(8,224)
Prepaid expenses	(69)	(284)	(1,690)
Other current assets	(343)	(138)	(693)
Deferred charges and other assets	(4,729)	(12,197)	(13,621)
Accounts payable	(3,613)	2,099	(1,571)
Income taxes receivable / payable	(2,972)	(81)	(1,066)
Accrued employee compensation and benefits	31,073	9,409	(6,418)
Other accrued expenses and current liabilities	(2,403)	3,465	449
Deferred revenue and customer liabilities	(2,759)	(4,521)	(1,623)
Other long-term liabilities	1,629	3,909	5,111
Operating lease assets and liabilities	(2,793)	834
Net cash provided by operating activities	175,742	101,283	109,094
Cash flows from investing activities:
Capital expenditures	(52,683)	(38,698)	(46,884)
Cash paid for business acquisitions, net of cash acquired	(88,466)	(3,133)	(78,395)
Proceeds from property and equipment insurance settlement		1,190
Purchase of intangible assets		(292)	(8,156)
Investment in equity method investees			(5,000)
Other	1,792	346	1,495
Net cash (used for) investing activities	(139,357)	(40,587)	(136,940)
Cash flows from financing activities:
Payments of long-term debt	(101,000)	(58,000)	(231,000)
Proceeds from issuance of long-term debt	91,000	29,000	58,000
Cash paid for repurchase of common stock	(52,176)	(30,281)
Proceeds from grants			31
Shares repurchased for tax withholding on equity awards	(1,827)	(3,214)	(3,687)
Cash paid for loan fees related to long-term debt		(1,098)
Net cash (used for) financing activities	(64,003)	(63,593)	(176,656)
Effects of exchange rates on cash, cash equivalents and restricted cash	2,829	1,851	(10,072)
Net increase (decrease) in cash, cash equivalents and restricted cash	(24,789)	(1,046)	(214,574)
Cash, cash equivalents and restricted cash – beginning	129,185	130,231	344,805
Cash, cash equivalents and restricted cash – ending	104,396	129,185	130,231
Supplemental disclosures of cash flow information:
Cash paid for amounts included in the measurement of operating lease liabilities under ASC 842	63,097	58,058
Cash paid during period for interest	1,423	3,500	3,888
Cash paid during period for income taxes	32,770	24,049	19,587
Non-cash transactions:
Net right-of-use assets arising from new or remeasured operating lease liabilities under ASC 842	16,799	30,014
Capital expenditures incurred but not yet paid	6,111	5,970	1,944
Unrealized gain (loss) on postretirement obligation, net of taxes, in accumulated other comprehensive income (loss)	(88)	$ 48	$ (80)
Property and equipment acquired under grant agreement	$ 1,612