Debt (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Term Loans [Abstract]
Term loans		$ 325,010,000	$ 263,014,000
Initiation date of loan agreement		Sep. 11, 2011
Periodic payments specified as percentage of drawn amount (in hundredths)		2.00%
Terms		The outstanding principal amounts under the term loan bear interest at the rate of LIBOR plus 2.5%, amortized quarterly, and require quarterly payments equal to 1.75% multiplied by the outstanding principal amount at such time. The facility contains various financial and other covenants.
Number of years in which specified amount of debt payable (in years)		5 years
Asset-Backed Warehouse Facility [Abstract]
Number of months based on which restricted cash is to be maintained (in months)		5 months
Capital Lease Obligations [Abstract]
Capital lease obligations		8,700,000
Collateralized Financing Obligations [Abstract]
Collateralized financing obligation		24,776,000	0
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Average interest rate (in hundredths)		3.00%
Amount outstanding under the facility		223,000,000
Revolving Credit Facility [Abstract]
Availability under the revolving credit facility		241,900,000
Balance reduced under the facility		100,000
Credit facility termination date		Sep. 25, 2014
Asset-Backed Warehouse Notes [Member]
Term Loans [Abstract]
Term loans		100,000,000
Interest rate at period end (in hundredths)		2.70%
Proceeds from facility drawn at closing		80,000,000
Asset-Backed Warehouse Facility [Abstract]
Proceeds from the facility	49,000,000		51,000,000
Number of initial years for which reference rate applied (in years)		2 years
Restricted cash		1,100,000
Term Loan [Member]
Debt Instrument [Line Items]
Maximum credit commitment		300,000,000
Average interest rate (in hundredths)		3.50%
Term Loans [Abstract]
Initiation date of loan agreement		Dec. 20, 2010
Capital Lease Obligations [Member]
Capital Lease Obligations [Abstract]
Capital lease obligations		8,700,000
Average interest rate on capital lease obligations (in hundredths)		3.30%
Letter of Credit [Member]
Debt Instrument [Line Items]
Maximum credit commitment		15,000,000
Swing Line Loans [Member]
Debt Instrument [Line Items]
Maximum credit commitment		10,000,000
Revolving Credit Facility [Abstract]
Number of business days in which short term borrowings are payable (in days)		10D
Collateralized Financing Obligation [Member]
Debt Instrument [Line Items]
Average interest rate (in hundredths)		3.30%
Collateralized Financing Obligations [Abstract]
Collateralized financing obligation		26,800,000
Maximum [Member] | Asset-Backed Warehouse Notes [Member]
Asset-Backed Warehouse Facility [Abstract]
Increased borrowing capacity, optional		200,000,000
Amortization of facility term (in years)		15 years
Minimum [Member] | Asset-Backed Warehouse Notes [Member]
Term Loans [Abstract]
Principal amount of loan		100,000,000
Asset-Backed Warehouse Facility [Abstract]
Amortization of facility term (in years)		10 years
Consortium of Banks [Member]
Term Loans [Abstract]
Term loans		268,100,000
Quarterly payments of principal		3,700,000
Number of quarterly installments		23
Debt instrument final payment		99,900,000
Debt instrument final payment in percentage (in hundredths)		54.00%
Numerator for calculation of quarterly payments of principal specified in percentage (in hundredths)		46.00%
Terms		The Base Rate is defined as the highest of (i) the federal funds rate plus 1/2 of 1.0%, (ii) the prime rate (as published in The Wall Street Journal),
Amount of loan repayable in one year		25,000,000
Consortium of Banks [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum credit commitment		465,000,000
Maximum amount credit facility might be increased		475,000,000
Consortium of Banks [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Maximum amount credit facility might be increased		100,000,000
Term Loans [Abstract]
Principal amount of loan		185,000,000
CAI Rail Inc [Member]
Debt Instrument [Line Items]
Maximum credit commitment		85,000,000
Amount outstanding under the facility		32,600,000
Revolving Credit Facility [Abstract]
Availability under the revolving credit facility		52,400,000
CAI Rail Inc [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Average interest rate (in hundredths)		2.70%
Consortium of banks, note dated April 11, 2012 [Member]
Debt Instrument [Line Items]
Average interest rate (in hundredths)		2.80%
Term Loans [Abstract]
Term loans		80,000,000
Initiation date of loan agreement		Apr. 11, 2012
Principal amount of loan		60,000,000
Periodic payments specified as percentage of outstanding amount (in hundredths)		1.75%
Development Bank of Japan [Member]
Term Loans [Abstract]
Term loans		7,800,000
Quarterly payments of principal		200,000
Number of quarterly installments		19
Debt instrument final payment		6,200,000
Number of years in which specified amount of debt payable (in years)		5 years
Interest rate at period end (in hundredths)		2.90%
Development Bank of Japan [Member] | Term Loan [Member]
Term Loans [Abstract]
Principal amount of loan		$ 10,000,000
Federal Funds Rate [Member] | Consortium of Banks [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Term Loans [Abstract]
Basis spread on variable rate (in hundredths)		1.25%
Federal Funds Rate [Member] | Consortium of Banks [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Term Loans [Abstract]
Basis spread on variable rate (in hundredths)		0.50%
Eurodollar Rate [Member] | Consortium of Banks [Member] | Term Loan [Member]
Term Loans [Abstract]
Basis spread on variable rate (in hundredths)		1.00%
LIBOR [Member] | Consortium of Banks [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Term Loans [Abstract]
Basis spread on variable rate (in hundredths)		2.25%
LIBOR [Member] | Consortium of Banks [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Term Loans [Abstract]
Basis spread on variable rate (in hundredths)		1.50%