Common Stock - Additional Information (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Common shares outstanding (in Shares)	3,691	3,693
Reissued shares during the period, shares (in Shares)	165	83	131