Stock Option Activity (Detail)	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Shares
Outstanding at beginning of year | shares	6,086,250
Granted | shares	831,000
Cancelled | shares	(10,000)
Expired | shares	(600,000)
Outstanding at end of year | shares	6,307,250
Exercisable at end of year | shares	5,224,082
Weighted-average exercise price
Outstanding at beginning of year | $ / shares	$ 22.32
Granted | $ / shares	20.06
Cancelled | $ / shares	16.59
Expired | $ / shares	26.06
Outstanding at end of year | $ / shares	21.68
Exercisable at end of year | $ / shares	$ 21.49