Condensed Consolidated Income Statements - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Condensed Consolidated Income Statements [Abstract]
Revenues (note 6)	$ 158,805	$ 155,477	$ 290,750	$ 271,095
Costs of services, excluding depreciation and amortization (note 7)	19,758	17,027	35,071	28,636
Gross revenue, net of expenses	139,047	138,450	255,679	242,459
Selling, general and administrative expenses (note 7)	74,595	65,239	142,902	128,995
Depreciation and amortization expenses (note 7)	10,284	10,769	20,364	21,385
Gain on disposition of property, plant and equipment	(201)	(791)	(447)	(966)
Foreign exchange loss (gain)	734	438	51	(2,769)
Operating income	53,635	62,795	92,809	95,814
Interest income	487	680	985	1,527
Interest expense	(1,060)	(1,308)	(2,423)	(2,577)
Equity income (note 18)	477	173	996	406
Other, net	269	918	967	1,631
Other income (expense)	173	463	525	987
Income before income taxes	53,808	63,258	93,334	96,801
Income tax expense (recovery) (note 8):
Current	16,106	19,365	26,115	30,078
Deferred	(2,889)	(1,953)	(3,366)	(3,233)
Income tax expense	13,217	17,412	22,749	26,845
Net income	40,591	45,846	70,585	69,956
Net income attributable to:
Stockholders	39,710	45,083	69,116	68,860
Non-controlling interests	$ 881	$ 763	$ 1,469	$ 1,096
Earnings per share attributable to stockholders (note 10):
Basic	$ 0.37	$ 0.42	$ 0.65	$ 0.64
Diluted	$ 0.37	$ 0.42	$ 0.65	$ 0.64
Weighted average number of shares outstanding (note 10):
Basic	106,245,307	106,506,916	106,581,294	106,993,228
Diluted	106,979,810	106,978,061	107,069,410	107,390,303