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Nature of Operations and Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
Bottom of range [Member]  
Disclosure of changes in accounting estimates [Line Items]  
Estimated useful life of property 30 years
Finite -Lived intangible assets, useful life 6 years
Capital asset, useful life 2 years
Bottom of range [Member] | Software [Member]  
Disclosure of changes in accounting estimates [Line Items]  
Finite -Lived intangible assets, useful life 3 years
Top of range [Member]  
Disclosure of changes in accounting estimates [Line Items]  
Estimated useful life of property 60 years
Finite -Lived intangible assets, useful life 68 years
Capital asset, useful life 10 years
Top of range [Member] | Software [Member]  
Disclosure of changes in accounting estimates [Line Items]  
Finite -Lived intangible assets, useful life 5 years