Commitments and Contingent Liabilities - Additional Information (Detail) - 3 months ended Mar. 31, 2018 kr in Thousands, $ in Thousands	USD ($) Bond	SEK (kr)
Commitments And Contingent Liabilities [Line Items]
Outstanding standby and commercial letters of credit \| $	$ 22,636
Akers AB [Member]
Commitments And Contingent Liabilities [Line Items]
Number of surety bonds issued \| Bond	2
Surety bonds issued to guarantee obligations	$ 4,000	kr 33,900

Sum of the amount of expected guaranteed benefits in excess of the projected account balances for minimum guaranteed benefit contracts, as of the balance sheet date, net of reinsurance recoverables, for all guaranteed benefit types.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389

Name:	us-gaap_GuaranteedBenefitLiabilityNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant