CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 22,944,000	$ 19,547,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property and equipment	10,792,000	10,222,000
Amortization of intangible assets	1,092,000	1,096,000
Accretion of closure and post-closure obligations	927,000	1,018,000
Unrealized foreign currency (gain) loss	1,706,000	(2,034,000)
Deferred income taxes	(1,646,000)	(785,000)
Share-based compensation expense	601,000	564,000
Unrecognized tax benefits	10,000	10,000
Net (gain) loss on sale of property and equipment	12,000	(34,000)
Changes in assets and liabilities:
Receivables	(7,218,000)	(1,994,000)
Income tax receivable		187,000
Other assets	(833,000)	(213,000)
Accounts payable and accrued liabilities	1,004,000	(3,485,000)
Deferred revenue	2,564,000	(112,000)
Accrued salaries and benefits	(1,541,000)	875,000
Income tax payable	2,752,000	515,000
Closure and post-closure obligations	(989,000)	(544,000)
Net cash provided by operating activities	32,177,000	24,833,000
Cash flows from investing activities:
Purchases of property and equipment	(15,590,000)	(12,433,000)
Business acquisition, net of cash acquired		(10,743,000)
Proceeds from sale of property and equipment	64,000	465,000
Restricted cash		5,000
Net cash used in investing activities	(15,526,000)	(22,706,000)
Cash flows from financing activities:
Payments on reducing revolving line of credit	(19,000,000)	(17,000,000)
Proceeds from reducing revolving line of credit	9,500,000	26,000,000
Proceeds from exercise of stock options	2,192,000
Deferred financing costs paid	(185,000)
Dividends paid	(6,645,000)	(9,850,000)
Other	(58,000)	(259,000)
Net cash used in financing activities	(14,196,000)	(1,109,000)
Effect of foreign exchange rate changes on cash	(197,000)	217,000
Increase in cash and cash equivalents	2,258,000	1,235,000
Cash and cash equivalents at beginning of period	2,120,000	4,289,000
Cash and cash equivalents at end of period	4,378,000	5,524,000
Supplemental Disclosures
Income taxes paid, net of receipts	11,467,000	12,155,000
Interest paid	547,000	616,000
Non-cash investing and financing activities:
Closure and post-closure retirement asset	550,000	956,000
Capital expenditures in accounts payable	2,526,000	973,000
Restricted stock issued from treasury shares	$ 864,000	$ 372,000