Significant Accounting Policies - Comprehensive Earnings Attributable to Noncontrolling Interests (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net earnings (loss) attributable to noncontrolling interests	$ 126	$ (38)	$ 143	$ (65)
Other comprehensive earnings, net of tax		1	1	2
Comprehensive earnings (loss) attributable to noncontrolling interests	$ 126	$ (37)	$ 144	$ (63)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669625-108580

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-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669619-108580

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-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569643-111683

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration