Summary of PSO Activity (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Shares Subject to Outstanding Stock Options
Ending balance | shares	5,817,116
Weighted-Average Exercise Price Per Share
Ending balance | $ / shares	$ 25.26
Performance Stock Options (PSOs)
Shares Subject to Outstanding Stock Options
Options granted | shares	271,122
Options canceled | shares	(90,370)
Ending balance | shares	180,752
Weighted-Average Exercise Price Per Share
Options granted | $ / shares	$ 23.76
Options canceled | $ / shares	23.76
Ending balance | $ / shares	$ 23.76