Employee Benefit Plans - Additional Information (Detail) (USD $)	3 Months Ended			1 Months Ended
	Dec. 31, 2012	Sep. 30, 2012 Helix Plan	Dec. 31, 2012 Nexus Plan	Jul. 25, 2011 Nexus Plan Risk Benefits (disability and death) Age	Jul. 25, 2011 Nexus Plan Pension Plans Age
Defined Benefit Plan Disclosure [Line Items]
Pension obligation, cash settlement	$ 87,000	$ 6,400,000
Accelerated amortization of prior pension losses		8,900,000	100,000
Minimum age for employees to be admitted into plan				17	24
Expected contribution			$ 500,000