Long-Term Debt (Narrative) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Credit available with FHLB	$ 2,675,044
Credit with FHLB used	88	100
Federal Home Loan Bank advances are scheduled to mature periodically through the year	2019
Effective interest rates, minimum	3.78%	0.99%	0.99%
Effective interest rates, maximum	4.19%	4.79%	4.79%
Prepaid FHLB advances		136,000
FHLB advances, yielding rate		2.36%
Prepayment penalties recorded in other non-interest expense		3,378
Weighted average interest rate on long-term subordinated debt	3.18%	3.85%	4.15%
Assumed other subordinated notes in conjunction with an acquisition	8,000
Amortizing adjustment over the life of the notes	$ 1,275
Subordinated notes, fixed-rate	8.00%
Percentage, redemption price must equal plus principal	100.00%
Assumed interest rate on convertible subordinated notes	5.00%
Conversion price per share	$ 12.50
Common stock reserved for issuance in convertible subordinated notes	47,200
Other Subordinated Notes [Member]
Debt Instrument [Line Items]
Subordinated notes maturity (year)	2016
Convertible Subordinated Notes [Member]
Debt Instrument [Line Items]
Subordinated notes maturity (year)	2018