Condensed Consolidated Income Statements - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Consolidated Income Statements [Abstract]
Revenues (note 6)	$ 166,186	$ 158,805	$ 290,685	$ 290,750
Costs of services, excluding depreciation and amortization (note 7)	21,591	19,758	34,404	35,071
Gross revenue, net of expenses	144,595	139,047	256,281	255,679
Selling, general and administrative expenses (note 7)	74,377	73,992	144,952	141,102
Acquisition-related costs (note 7)	22,948	603	31,575	1,800
Depreciation and amortization expenses (note 7)	11,872	10,284	22,210	20,364
Gain on disposition of property, plant and equipment	(308)	(201)	(1,029)	(447)
Impairment loss (note 7)	8,911		8,911
Foreign exchange loss (gain)	(93)	734	(823)	51
Operating income	26,888	53,635	50,485	92,809
Other income (expense):
Interest income	987	487	1,942	985
Interest expense	(8,620)	(1,060)	(16,753)	(2,423)
Equity income (loss) (note 17)	4	477	(49)	996
Other, net	2,479	269	3,861	967
Other income (expense)	(5,150)	173	(10,999)	525
Income before income taxes	21,738	53,808	39,486	93,334
Income tax expense (recovery) (note 8):
Current	8,675	16,106	16,163	26,115
Deferred	(4,650)	(2,889)	(4,823)	(3,366)
Income tax expense	4,025	13,217	11,340	22,749
Net income	17,713	40,591	28,146	70,585
Net income attributable to:
Stockholders	17,635	39,710	28,012	69,116
Non-controlling interests	$ 78	$ 881	$ 134	$ 1,469
Earnings per share attributable to stockholders (note 9):
Basic	$ 0.16	$ 0.37	$ 0.26	$ 0.65
Diluted	$ 0.16	$ 0.37	$ 0.26	$ 0.65
Weighted average number of shares outstanding (note 9):
Basic	107,004,902	106,245,307	106,928,672	106,581,294
Diluted	108,238,660	106,979,810	108,014,228	107,069,410