Significant Accounting Policies - Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2017
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life	39 years
Capital improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Capital improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	20 years
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years