Condensed Consolidated Income Statements - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue:
Total revenue	$ 303,429	$ 260,178
Operating expenses:
Direct expenses	36,069	36,657
Selling, general and administrative expenses	95,184	97,470
Acquisition-related costs	669	1,633
Depreciation and amortization expenses	17,115	16,191
Gain on disposition of property, plant and equipment	(149)	(345)
Foreign exchange (gain) loss	478	(92)
Total operating expenses	269,841	227,305
Operating income	33,588	32,873
Interest expense	(10,816)	(11,310)
Other income, net	2,039	913
Income before income taxes	24,811	22,476
Income tax expense	6,639	5,269
Net income	18,172	17,207
Net income attributable to:
Stockholders	18,164	17,138
Non-controlling interests	8	69
Net income	$ 18,172	$ 17,207
Earnings per share attributable to stockholders:
Basic	$ 0.17	$ 0.16
Diluted	$ 0.17	$ 0.16
Weighted average number of shares outstanding:
Basic	108,765,489	107,355,381
Diluted	110,044,213	108,643,897
Service Revenues [Member]
Revenue:
Total revenue	$ 172,372	$ 176,016
Operating expenses:
Direct expenses	36,069	36,657
Inventory Sales Revenue [Member]
Revenue:
Total revenue	131,057	84,162
Operating expenses:
Direct expenses	$ 120,475	$ 75,791