Stock Option Activity (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Shares
Outstanding at beginning of year | shares	6,307,250
Granted | shares	969,900
Exercised | shares	(40,000)
Expired | shares	(550,000)
Outstanding at end of year | shares	6,687,150
Exercisable at end of year | shares	5,326,606
Weighted-average exercise price
Outstanding at beginning of year | $ / shares	$ 21.68
Granted | $ / shares	18.40
Exercised | $ / shares	17.69
Expired | $ / shares	28.26
Outstanding at end of year | $ / shares	20.68
Exercisable at end of year | $ / shares	$ 21.01