Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net income	$ 75,948,000	$ 72,303,000
Adjustments for items not affecting cash:
Depreciation and amortization expenses	37,150,000	34,227,000
Stock option compensation expense	2,730,000	3,199,000
Equity-classified share unit expense	5,017,000	5,903,000
Deferred income tax expense	6,657,000	1,056,000
Unrealized foreign exchange (gain) loss	1,129,000	(51,000)
Gain on disposition of property, plant and equipment	(1,260,000)	(250,000)
Amortization of debt issuance costs	1,577,000	1,765,000
Amortization of right-of-use assets	6,318,000	5,845,000
Gain on contingent consideration from equity investment	(1,700,000)
Other, net	1,934,000	322,000
Net changes in operating assets and liabilities	62,824,000	36,036,000
Net cash provided by operating activities	198,324,000	160,355,000
Investing activities:
Property, plant and equipment additions	(6,140,000)	(4,618,000)
Intangible asset additions	(13,244,000)	(12,175,000)
Proceeds on disposition of property, plant and equipment	16,106,000	583,000
Distribution from equity investment	4,212,000
Proceeds on contingent consideration from equity investment	1,700,000
Other, net	(2,782,000)	(1,000,000)
Net cash used in investing activities	(148,000)	(17,210,000)
Financing activities:
Share repurchase	(53,170,000)	(42,012,000)
Dividends paid to stockholders	(43,586,000)	(39,160,000)
Issuances of share capital	19,425,000	4,124,000
Payment of withholding taxes on issuance of shares	(3,321,000)	(4,915,000)
Proceeds from short-term debt	35,799,000	12,879,000
Repayment of short-term debt	(19,941,000)	(24,985,000)
Repayment of long-term debt	(8,633,000)	(14,514,000)
Repayment of finance lease obligations	(4,384,000)	(2,937,000)
Net cash used in financing activities	(77,811,000)	(111,520,000)
Effect of changes in foreign currency rates on cash, cash equivalents, and restricted cash	(2,608,000)	1,802,000
Increase	117,757,000	33,427,000
Beginning of period	420,256,000	305,567,000
Cash, cash equivalents, and restricted cash, end of period	$ 538,013,000	$ 338,994,000