Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income before income taxes and non-controlling interest [Abstract]
U.S. operations	$ 15,595,000	$ 21,909,000	$ 11,276,000
Foreign operations	58,504,000	39,989,000	20,481,000
Net income before income taxes and non-controlling interest	74,099,000	61,898,000	31,757,000
Current [Abstract]
Federal	1,557,000	6,261,000	(607,000)
State	38,000	29,000	32,000
Foreign	2,209,000	1,241,000	772,000
Current income tax expense (benefit)	3,804,000	7,531,000	197,000
Deferred [Abstract]
Federal	5,297,000	2,623,000	2,739,000
State	(257,000)	89,000	92,000
Foreign	974,000	841,000	527,000
Deferred income tax expense (benefit)	6,014,000	3,553,000	3,358,000
Income tax expense	9,818,000	11,084,000	3,555,000
Computed tax benefit at federal statutory rate (in hundredths)	35.00%
Effective income tax rate reconciliation [Abstract]
Computed expected tax expense	25,935,000	21,668,000	11,116,000
Non-deductible stock-based compensation	86,000	68,000	80,000
Provision to tax return true-up	(148,000)	8,000	(261,000)
Other permanent differences	1,383,000	920,000	88,000
Increase (release) of uncertain tax liabilities	(78,000)	185,000	(1,919,000)
Increase (decrease) in income taxes resulting from [Abstract]
State income tax expense, net of federal income tax benefit	(66,000)	154,000	321,000
Foreign tax differential	(17,294,000)	(11,919,000)	(5,870,000)
Income tax expense	9,818,000	11,084,000	3,555,000
Deferred tax assets [Abstract]
Accounts receivable (owned fleet)	179,000	181,000
Accrued expenses and other current liabilities	78,000	71,000
State taxes	1,000	1,000
Unearned revenue	1,983,000	1,753,000
Stock-based compensation	1,540,000	1,214,000
Interest expense	6,000	6,000
Tax credits	8,000	161,000
Net operating loss carry forwards	1,562,000	574,000
Gross deferred tax assets	5,357,000	3,961,000
Deferred tax liabilities [Abstract]
Intangible assets	296,000	527,000
Depreciation and amortization	36,817,000	30,717,000
Foreign deferred tax liabilities	3,222,000	2,937,000
Deferred subpart F income	2,832,000	1,590,000
Unrealized gain or (loss)	52,000	38,000
Net deferred tax liability	37,862,000	31,848,000
Undistributed foreign earnings	126,800,000
Activities related to unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits. beginning balance	256,000	77,000
Decreases related to prior year tax positions		56,000
Increases related to prior year tax positions	7,000
Increases related to current year tax positions	31,000	123,000
Decreases related to lapsing of statute	(72,000)
Decreases related to settlement	(40,000)
Unrecognized tax benefits, ending balance	182,000	256,000	77,000
Accrued interest and penalities relating to unrecognized tax benefits	100,000	100,000
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	34,600,000
Expiration date	2017
State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 7,600,000
Expiration date	2029