Benefit Plans - Stock Options Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Shares, Outstanding at beginning of year	2,322,593		2,860,081		3,000,406
Shares, Assumed in acquisition	0	[1]	0	[1]	356,490	[1]
Shares, Exercised	0		0		(1,019)
Shares, Forfeited or expired	(494,002)		(537,488)		(495,796)
Shares, Outstanding at end of year	1,828,591		2,322,593		2,860,081
Shares, Exercisable at year-end	1,828,591		2,320,696		2,756,007
Weighted Average Exercise Price, Outstanding at beginning of year (in usd per share)	$ 17		$ 17		$ 17
Weighted Average Exercise Price, Assumed in acquisition (in usd per share)	$ 0	[1]	$ 0	[1]	$ 17	[1]
Weighted Average Exercise Price, Exercised (in usd per share)	$ 0		$ 0		$ 12
Weighted Average Exercise Price, Forfeited or expired (in usd per share)	$ 19		$ 19		$ 16
Weighted Average Exercise Price, Outstanding at end of year (in usd per share)	$ 17		$ 17		$ 17
Weighted Average Exercise Price, Exercisable at year-end (in usd per share)	$ 17		$ 17		$ 18

[1] Stock options acquired in connection with the State Bancorp acquisition.