Financial Instruments - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Financial Instrument [Line Items]
Estimated fair value of contingent liability	$ 0
Standby Letters of Credit
Financial Instrument [Line Items]
Fair value of contingent liability	1,222,000	$ 2,430,000
Performance Bonds
Financial Instrument [Line Items]
Fair value of contingent liability	$ 3,600,000	$ 4,000,000

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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