Common Stock and Earnings Per Share - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	May 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 29, 2015
Earnings Per Share [Abstract]
Business acquisition, common shares issued	3,500,000
Business acquisition date	May 31, 2015
Conversion of Company's common stock due to merger	9.2295
Market value common stock issued	$ 179.7
Closing stock price					$ 51.79
Common stock share repurchase program, number of shares authorized to be repurchased		2,000,000	2,000,000	2,000,000