CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 18,370	$ 12,584	$ 13,970
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property and equipment	13,933	7,750	7,879
Amortization of intangible assets	1,419	231
Accretion of closure and post-closure obligations	1,292	1,137	1,167
Unrealized foreign currency loss (gain)	1,324	(1,205)
Deferred income taxes	(1,095)	(286)	1,793
Stock-based compensation expense	837	988	655
Unrecognized tax benefits	454
Net loss on sale of property and equipment	187	171	296
Investment premium amortization		20
Accretion of interest income		(2)
Changes in assets and liabilities (net of effect of business acquisition):
Receivables	3,593	(11,278)	14,435
Income tax receivable	(188)		2,834
Other assets	715	(618)	(11)
Accounts payable and accrued liabilities	2,880	1,702	(1,054)
Deferred revenue	(21)	339	(3,304)
Accrued salaries and benefits	1,389	1,141	(1,160)
Income tax payable	(1,106)	2,413	201
Closure and post-closure obligations	(792)	(158)	(928)
Other			14
Net cash provided by operating activities	43,191	14,929	36,787
Cash flows from investing activities:
Purchases of property and equipment	(10,096)	(14,190)	(9,405)
Proceeds from sale of property and equipment	98	58	64
Business acquisition (net of cash acquired)		(77,427)
Purchases of short-term investments		(4,998)	(1,409)
Maturities of short-term investments		6,375
Restricted cash		685	(84)
Net cash used in investing activities	(9,998)	(89,497)	(10,834)
Cash flows from financing activities:
Payments on reducing revolving line of credit	(39,400)
Dividends paid	(13,113)	(13,090)	(13,068)
Proceeds from reducing revolving line of credit	16,900	63,000
Other	449	45	(11)
Deferred financing costs paid		(373)
Net cash (used in) provided by financing activities	(35,164)	49,582	(13,079)
Effect of foreign exchange rate changes on cash	(82)	(19)
(Decrease) increase in cash and cash equivalents	(2,053)	(25,005)	12,874
Cash and cash equivalents at beginning of year	6,342	31,347	18,473
Cash and cash equivalents at end of year	$ 4,289	$ 6,342	$ 31,347