Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		1 Months Ended
	Mar. 31, 2012 Helix Plan	Jun. 30, 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	$ 6
Pension obligation, accelerated amortization	8
Expected contribution	$ 0.7	$ 0.3
Minimum age for employees to be admitted into plan			17	24