Changes in Nonvested Stock Options (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share
Nonvested stock options outstanding, at beginning of the year	3,303,826
Granted	386,749
Vested	(1,579,414)
Forfeited or Cancelled	(82,601)
Nonvested stock options outstanding, at end of the year	2,028,560	3,303,826
Weighted-average grant-date fair value per share
Nonvested stock options weighted average grant date fair value at beginning of the year	$ 13.40
Granted	$ 16.22	$ 12.80	$ 11.54
Vested	$ 13.85
Forfeited or Cancelled	$ 13.09
Nonvested stock options weighted average grant date fair value at end of the year	$ 13.60	$ 13.40