Consolidated Income Statements - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Income Statements [Abstract]
Revenues (note 5)	$ 610,517	$ 566,395	$ 515,875
Costs of services, excluding depreciation and amortization (note 6)	79,013	66,062	56,026
Gross revenue, net of expenses	531,504	500,333	459,849
Selling, general and administrative expenses (note 6)	323,270	283,529	254,389
Acquisition-related costs (note 6)	38,272	11,829	601
Depreciation and amortization expenses (note 6)	52,694	40,861	42,032
Gain on disposition of property, plant and equipment	(1,656)	(1,282)	(9,691)
Impairment loss (note 7)	8,911	28,243
Foreign exchange loss (gain)	2,559	1,431	(2,322)
Operating income	107,454	135,722	174,840
Other income (expense):
Interest income	3,194	1,863	2,660
Interest expense	(38,291)	(5,564)	(4,962)
Debt extinguishment costs		(6,787)
Equity income (loss) (note 22)	(26)	1,028	916
Other, net	5,063	4,232	2,982
Other income (expense)	(30,060)	(5,228)	1,596
Income before income taxes	77,394	130,494	176,436
Income tax expense (recovery) (note 8):
Current	19,356	40,341	42,420
Deferred	(17,268)	(3,359)	(4,559)
Income tax expense	2,088	36,982	37,861
Net income	75,306	93,512	138,575
Net income attributable to:
Stockholders	75,027	91,832	136,214
Non-controlling interests	$ 279	$ 1,680	$ 2,361
Earnings per share attributable to stockholders (note 10):
Basic	$ 0.70	$ 0.86	$ 1.27
Diluted	$ 0.69	$ 0.85	$ 1.27
Weighted average number of shares outstanding (note 10):
Basic	107,044,348	106,630,323	107,075,845
Diluted	108,113,151	107,457,794	107,432,474