Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	6 Months Ended		6 Months Ended	0 Months Ended	1 Months Ended	6 Months Ended	12 Months Ended		1 Months Ended
	Jan. 16, 2014	Jun. 30, 2014 LetterOfCredit	Feb. 14, 2012	Jun. 30, 2014 New Hampshire [Member]	May 31, 2014 Apollo and Parks Township [Member] Claim	Dec. 31, 2009 Apollo and Parks Township [Member]	Jun. 30, 2014 Apollo and Parks Township [Member] Cases Claim Facility	Dec. 31, 2008 Apollo and Parks Township [Member]	Dec. 31, 1998 Apollo and Parks Township [Member]	Dec. 31, 2009 Apollo and Parks Township [Member] Personal Injury and Wrongful Death Claims [Member] Claim	Dec. 31, 2009 Apollo and Parks Township [Member] Property Damage Claims [Member] Claim	Jun. 30, 2014 Apollo and Parks Township [Member] 2008 Settlement [Member]	Jun. 30, 2014 Apollo and Parks Township [Member] 2009 Settlement [Member]
Contingencies And Commitments [Line Items]
Number of claimants							100
Number of facilities							2
Number of cases consolidated for most non-dispositive pre-trial matters							15
Number of filed motions to dismiss, with prejudice							3
Number of claims agreed to dismiss, with prejudice							3
Number of additional claims					5
Aggregate settlement amount for claims						$ 52.5		$ 27.5	$ 8.0
Number of claims settled										250	125
Percentage of ARCO's recovery amounts assigned to company							58.33%
Interest accrued on settlement												8.8	6.2
Interest rate on settlement			6.00%
Appeal bond required as a percentage of total judgment			120.00%
Amount capped under the contract		18.7
Five partial draws		9
Total partial draws against letter of credit from Bwcc		11.0
Total draws of Letter of Credit in LDs		11.9
Partial draws available against letter of credit from Bwcc		44
Aggregate liquidated damages cap		37.4
Total provisions in financial statements		12.8
Damages in excess	37
Recovery of damages incurred				$ 50