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Investment Properties - Estimated Service Lives of Investment Properties (Detail)
12 Months Ended
Dec. 31, 2017
Land improvements [Member] | Bottom of range [Member]  
Disclosure of detailed information about investment property [Line Items]  
Estimated service lives P8Y
Land improvements [Member] | Top of range [Member]  
Disclosure of detailed information about investment property [Line Items]  
Estimated service lives P30Y
Main buildings [Member] | Bottom of range [Member]  
Disclosure of detailed information about investment property [Line Items]  
Estimated service lives P35Y
Main buildings [Member] | Top of range [Member]  
Disclosure of detailed information about investment property [Line Items]  
Estimated service lives P60Y
Other building facilities [Member] | Bottom of range [Member]  
Disclosure of detailed information about investment property [Line Items]  
Estimated service lives P4Y
Other building facilities [Member] | Top of range [Member]  
Disclosure of detailed information about investment property [Line Items]  
Estimated service lives P10Y