Shareholders' Equity - Summary of Outstanding Shares of Common Stock (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Shares outstanding at beginning of year	43,550	43,420	43,054
Treasury shares issued for:
Restricted stock awards	28	108	206
401(k) plan			134
Employee stock options exercised	36	22	26
Shares outstanding at end of year	43,614	43,550	43,420