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Employee Benefit Plans - Additional Information (Detail) kr in Millions	1 Months Ended	3 Months Ended				6 Months Ended
	May 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 NOK (kr)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 NOK (kr)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 NOK (kr)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 NOK (kr)
President, and Chief Executive Officer [Member] | Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Settlement of distribution	$ 8,900,000
Settlement loss		$ 300,000
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, employer contributions		0		$ 0		$ 0		$ 0
Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, employer contributions		40,000		0		300,000		0
Expected contribution to the plan during the remaining quarters of fiscal 2018		700,000				700,000
Norway’s Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, employer contributions		200,000	kr 1.9	$ 400,000	kr 3.0	200,000	kr 1.9	$ 400,000	kr 3.0
Expected contribution to the plan during the remaining quarters of fiscal 2018		$ 0				$ 0

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