Consolidated Income Statements - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Income Statements [Abstract]
Revenues (note 5)	$ 515,875	$ 481,097	$ 467,403
Direct expenses, excluding depreciation and amortization (note 6)	56,026	57,884	54,008
Gross revenue, net of expenses	459,849	423,213	413,395
Selling, general and administrative expenses (note 6)	254,990	248,220	243,736
Depreciation and amortization expenses (note 6)	42,032	44,536	43,280
Gain on disposition of property, plant and equipment	(9,691)	(3,512)	(10,552)
Impairment loss (note 6)		8,084
Foreign exchange gain	(2,322)	(2,042)	(28)
Operating income	174,840	127,927	136,959
Interest income	2,660	2,222	2,708
Interest expense	(4,962)	(5,277)	(7,434)
Equity income (note 20)	916	458	405
Other, net	2,982	3,708	2,117
Other income (expense)	1,596	1,111	(2,204)
Income before income taxes	176,436	129,038	134,755
Income tax expense (note 7):
Current	42,420	33,321	36,909
Deferred	(4,559)	3,154	3,401
Income tax expense	37,861	36,475	40,310
Net income	138,575	92,563	94,445
Net income attributable to:
Shareholders	136,214	90,981	93,644
Non-controlling interests	$ 2,361	$ 1,582	$ 801
Earnings per share attributable to shareholders (note 9):
Basic	$ 1.27	$ 0.85	$ 0.88
Diluted	$ 1.27	$ 0.85	$ 0.87
Weighted average number of shares outstanding (note 9):
Basic	107,075,845	107,268,425	106,768,856
Diluted	107,432,474	107,654,828	107,155,173