Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Flows from Operating Activities:
Net Income	$ 44,777	$ 49,602	$ 36,479
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation and Amortization	72,476	67,395	62,577
Provision for Doubtful Accounts	4,263	1,755	1,494
Non-Cash Stock-Based Compensation	3,840	5,221	4,227
Gain on Sale of Used Rental Equipment	(12,389)	(12,444)	(11,728)
Change In:
Accounts Receivable	(3,848)	(17,938)	(7,385)
Income Taxes Receivable		6,131	120
Prepaid Expenses and Other Assets	(2,337)	(3,226)	296
Accounts Payable and Accrued Liabilities	(3,456)	5,715	3,399
Deferred Income	1,857	1,277	(954)
Deferred Income Taxes	21,198	25,823	12,073
Net Cash Provided by Operating Activities	126,381	129,311	100,598
Cash Flows from Investing Activities:
Payments Related to Acquisition of Adler Tanks			(39)
Purchase of Rental Equipment	(131,805)	(154,963)	(122,749)
Purchase of Property, Plant and Equipment	(14,161)	(17,204)	(12,144)
Proceeds from Sale of Used Rental Equipment	30,970	28,453	28,694
Net Cash Used in Investing Activities	(114,996)	(143,714)	(106,238)
Cash Flows from Financing Activities:
Net Borrowings (Repayments) Under Bank Lines of Credit	5,500	(57,140)	30,306
Borrowings Under Private Placement		100,000
Principal Payments on Senior Notes		(12,000)	(12,000)
Proceeds from the Exercise of Stock Options	5,591	5,054	7,506
Excess Tax Benefit from Exercise and Disqualifying Disposition of Stock Options	1,033	980	1,021
Payment of Dividends	(23,126)	(22,252)	(21,390)
Net Cash Provided by (Used in) Financing Activities	(11,002)	14,642	5,443
Net Increase (Decrease) in Cash	383	239	(197)
Cash Balance, beginning of period	1,229	990	1,187
Cash Balance, end of period	1,612	1,229	990
Interest Paid, during the period	9,107	6,877	6,306
Income Taxes Paid (Refunds Received), during the period	5,842	(1,480)	9,342
Dividends Accrued During the period, not yet paid	6,194	5,952	5,513
Rental Equipment Acquisitions, not yet paid	$ 4,491	$ 8,186	$ 5,388