Stock Option Activity (Detail)	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Underlying Shares
Outstanding at beginning of period | shares	6,687,150
Exercised | shares	(10,000)
Expired | shares	(600,000)
Outstanding at end of period | shares	6,077,150
Exercisable at end of year | shares	5,271,650
Weighted Average Exercise Price Per Share
Outstanding at beginning of period | $ / shares	$ 20.68
Exercised | $ / shares	22.29
Expired | $ / shares	24.17
Outstanding at end of period | $ / shares	20.34
Exercisable at end of year | $ / shares	$ 20.53