Other Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Other Assets [Line Items]
Gross carrying amount of intangible assets	$ 47.4	$ 45.1
Amortization expense related to intangible assets	2.9	1.5	$ 1.4
Intangible lease value
Schedule of Other Assets [Line Items]
Gross carrying amount of intangible assets	$ 41.6	$ 40.5