Annual report pursuant to Section 13 and 15(d)

Dividends (Parenthetical) (Detail)

v3.8.0.1
Dividends (Parenthetical) (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]      
Effective Date of change in amount of quarterly dividend Feb. 23, 2017 Feb. 24, 2016  
Revised quarterly dividend $ 0.29 $ 0.27  
Dividends related to outstanding restricted stock units $ 593 $ 554 $ 558