Commitments and Contingencies - Additional Information (Detail) (USD $)	Jun. 30, 2012
Guarantee Payment Of Insurance Claims
Commitments and Contingencies Disclosure [Line Items]
Letters of credit outstanding	$ 45,146,000
Current Investments
Commitments and Contingencies Disclosure [Line Items]
Investments providing collateral for letters of credit to guarantee insurance claims	36,601,000
Non-Current Investments
Commitments and Contingencies Disclosure [Line Items]
Investments providing collateral for letters of credit to guarantee insurance claims	13,561,000
Credit Agreement
Commitments and Contingencies Disclosure [Line Items]
Letters of credit outstanding	$ 33,552,000