Condensed Consolidated Income Statements - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Total revenue	$ 331,555,000	$ 273,255,000
Operating expenses:
Selling, general and administrative expenses	116,078,000	98,385,000
Acquisition-related costs	2,922,000
Depreciation and amortization expenses	21,070,000	19,293,000
Gain on disposition of property, plant and equipment	(68,000)	(47,000)
Foreign exchange loss	277,000	602,000
Total operating expenses	287,053,000	239,173,000
Operating income	44,502,000	34,082,000
Interest expense	(8,946,000)	(9,182,000)
Other income, net	1,002,000	3,577,000
Income before income taxes	36,558,000	28,477,000
Income tax expense	8,419,000	5,648,000
Net income	28,139,000	22,829,000
Net income attributable to:
Stockholders	28,188,000	22,809,000
Non-controlling interests	(49,000)	20,000
Net income	$ 28,139,000	$ 22,829,000
Earnings per share attributable to stockholders:
Basic	$ 0.26	$ 0.21
Diluted	$ 0.25	$ 0.21
Weighted average number of shares outstanding:
Basic	109,972,997	109,248,880
Diluted	111,267,392	110,482,837
Service Revenue [Member]
Revenues:
Total revenue	$ 206,030,000	$ 183,123,000
Operating expenses:
Direct expenses	36,027,000	39,355,000
Inventory Sales Revenue [Member]
Revenues:
Total revenue	125,525,000	90,132,000
Operating expenses:
Direct expenses	$ 110,747,000	$ 81,585,000