Changes in Nonvested Stock Options (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share
Nonvested stock options outstanding, at beginning of the year (in shares)	2,028,560
Granted (in shares)	505,770
Vested (in shares)	(1,161,865)
Forfeited or Cancelled (in shares)	(31,579)
Nonvested stock options outstanding, at end of the year (in shares)	1,340,886	2,028,560
Weighted-average grant-date fair value per share
Nonvested stock options weighted average grant date fair value at beginning of the year (in dollars per share)	$ 13.60
Granted (in dollars per share)	18.72	$ 16.22	$ 12.80
Vested (in dollars per share)	13.79
Forfeited or Cancelled (in dollars per share)	14.87
Nonvested stock options weighted average grant date fair value at end of the year (in dollars per share)	$ 15.12	$ 13.60