Annual report pursuant to Section 13 and 15(d)

Summary of Potential Number of Units that Could Vest Under Restricted Stock Unit Awards (Parenthetical) (Detail)

v3.6.0.2
Summary of Potential Number of Units that Could Vest Under Restricted Stock Unit Awards (Parenthetical) (Detail) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Restricted Stock Units (RSUs)      
Schedule of Restricted Stock Unit [Line Items]      
Weighted average market value on grant dates $ 29.83 $ 43.19 $ 28.54