CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES:
Net income	$ 60,801	$ 64,743	$ 74,564
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	110,730	88,945	72,665
Non-cash impairment charges	4,941	3,290	0
Deferred income tax benefit	(8,184)	(67,304)	(6,474)
Share-based compensation	20,779	21,550	17,310
Amortization of debt issuance costs	6,270	2,722	2,529
Non-cash interest expense	0	0	8,074
Realized loss on sale of short-term investments	0	2,287	0
Loss on disposal of property and equipment	1,385	6,989	1,765
Gain on divestiture of business	0	(2,645)	0
Change in fair value of contingent consideration and others	1,214	(4,710)	(13)
Payment of accreted interest	0	0	(42,786)
Changes in assets and liabilities, net of business acquisitions:
Accounts receivable	(17,021)	(89,698)	(17,518)
Inventories	8,300	99	(9,576)
Prepaid expenses and other current assets	3,933	(33,808)	14,912
Other non-current assets	1,052	(914)	(475)
Accounts payable, accrued expenses and other current liabilities	3,588	95,321	(414)
Deferred revenue	1,504	3,874	1,251
Other non-current liabilities	391	23,803	591
Net cash provided by operating activities	199,683	114,544	116,405
INVESTING ACTIVITIES:
Change in restricted cash	0	0	4,165
Proceeds from sale of short-term investments	0	16,951	0
Proceeds from note receivable	910	483	0
Cash used in business acquisitions, net of cash acquired	26,704	(1,241,946)	225
Purchases of property and equipment	(77,741)	(43,503)	(47,328)
Proceeds from sales of property and equipment	422	293	316
Proceeds from divestiture of business	0	46,387	0
Net cash used in investing activities	(49,705)	(1,221,335)	(42,622)
FINANCING ACTIVITIES:
Proceeds from borrowings of long-term indebtedness	171,200	1,307,000	680,000
Payments on debt	(660,000)	(117,000)	(511,250)
Net cash paid for contingent consideration	(38,196)	(4,661)	0
Proceeds from the issuance of common stock, net of issuance costs	349,590	0	0
Payment of liability component of convertible notes	0	0	(184,313)
Payment of capital lease obligation	0	0	(653)
Debt issuance costs	(5,037)	(19,043)	(4,530)
Proceeds from exercised stock options	9,392	9,774	10,481
Cash taxes paid in net equity settlement	(7,821)	(7,123)	(4,851)
Net cash provided by (used in) financing activities	(180,872)	1,168,947	(15,116)
Effect of exchange rate changes on cash and cash equivalents	(5,203)	10,724	(4,744)
Net increase (decrease) in cash and cash equivalents	(36,097)	72,880	53,923
Cash and cash equivalents at beginning of period	174,935	102,055	48,132
Cash and cash equivalents at end of period	$ 138,838	$ 174,935	$ 102,055