Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Percentage of comparable consolidated amounts	95.00%	95.00%
ASU 2016-01 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Decrease in net income	$ 390
ASU 2016-01 [Member] | Common Shares [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Decrease in diluted earnings per common share	$ 0.02