Fair Value Of Assets And Liabilities (Summary Of Carrying Amounts And Estimated Fair Values Of Financial Instruments) (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest bearing deposits with banks	$ 685,302,000	$ 1,035,743,000		$ 900,755,000
Available-for-sale securities	1,870,831,000	1,796,076,000		1,869,344,000
Trading account securities	1,036,000	583,000		1,140,000
Brokerage customer receivables	25,614,000	24,864,000		31,085,000
Mortgage loans held-for-sale, at lower of cost or market	10,352,000	27,167,000		10,728,000
FDIC Indemnification asset	170,696,000	208,160,000		263,212,000	344,251,000
Federal Home Loan Bank advances	414,032,000	414,122,000		466,391,000
Subordinated notes	15,000,000	15,000,000		35,000,000
Other borrowings	256,244,000	274,411,000		411,037,000
Secured borrowings-owed to securitization investors	0	0	360,800,000	428,000,000
Junior subordinated debentures	249,493,000	249,493,000		249,493,000
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	213,201,000	315,028,000		160,602,000
Interest bearing deposits with banks	685,302,000	1,035,743,000		900,755,000
Available-for-sale securities	1,870,831,000	1,796,076,000		1,869,344,000
Trading account securities	1,036,000	583,000		1,140,000
Brokerage customer receivables	25,614,000	24,864,000		31,085,000
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	76,601,000	79,564,000		88,216,000
Mortgage loans held-for-sale, at fair value	370,570,000	385,033,000		339,600,000
Mortgage loans held-for-sale, at lower of cost or market	10,352,000	27,167,000		10,728,000
Total loans	12,418,973,000	12,389,030,000		11,408,604,000
Mortgage servicing rights	7,344,000	6,750,000		7,201,000
Nonqualified deferred compensation assets	6,545,000	5,532,000		5,315,000
Derivative assets	52,436,000	53,906,000		39,220,000
FDIC Indemnification asset	170,696,000	208,160,000		263,212,000
Accrued interest receivable and other	156,825,000	157,157,000		153,755,000
Total financial assets	16,066,326,000	16,484,593,000		15,278,777,000
Non-maturity deposits	9,293,104,000	9,447,633,000		7,841,467,000
Deposits with stated maturities	4,669,653,000	4,980,911,000		4,824,386,000
Notes payable	31,911,000	2,093,000		52,639,000
Federal Home Loan Bank advances	414,032,000	414,122,000		466,391,000
Subordinated notes	15,000,000	15,000,000		35,000,000
Other borrowings	256,244,000	274,411,000		411,037,000
Secured borrowings-owed to securitization investors	0	0		428,000,000
Junior subordinated debentures	249,493,000	249,493,000		249,493,000
Derivative liabilities	54,745,000	57,751,000		46,364,000
Accrued interest payable and other	11,520,000	11,589,000		11,531,000
Total financial liabilities	14,995,702,000	15,453,003,000		14,366,308,000
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	213,201,000	315,028,000		160,602,000
Interest bearing deposits with banks	685,302,000	1,035,743,000		900,755,000
Available-for-sale securities	1,870,831,000	1,796,076,000		1,869,344,000
Trading account securities	1,036,000	583,000		1,140,000
Brokerage customer receivables	25,614,000	24,864,000		31,085,000
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	76,601,000	79,564,000		88,216,000
Mortgage loans held-for-sale, at fair value	370,570,000	385,033,000		339,600,000
Mortgage loans held-for-sale, at lower of cost or market	10,458,000	27,568,000		10,905,000
Total loans	13,125,643,000	13,053,101,000		11,798,811,000
Mortgage servicing rights	7,344,000	6,750,000		7,201,000
Nonqualified deferred compensation assets	6,545,000	5,532,000		5,315,000
Derivative assets	52,436,000	53,906,000		39,220,000
FDIC Indemnification asset	170,696,000	208,160,000		263,212,000
Accrued interest receivable and other	156,825,000	157,157,000		153,755,000
Total financial assets	16,773,102,000	17,149,065,000		15,669,161,000
Non-maturity deposits	9,293,104,000	9,447,633,000		7,841,467,000
Deposits with stated maturities	4,701,049,000	5,013,757,000		4,859,697,000
Notes payable	31,911,000	2,093,000		52,639,000
Federal Home Loan Bank advances	425,103,000	425,431,000		498,504,000
Subordinated notes	15,000,000	15,000,000		35,000,000
Other borrowings	256,244,000	274,411,000		411,037,000
Secured borrowings-owed to securitization investors	0	0		430,044,000
Junior subordinated debentures	250,470,000	250,428,000		177,355,000
Derivative liabilities	54,745,000	57,751,000		46,364,000
Accrued interest payable and other	11,520,000	11,589,000		11,531,000
Total financial liabilities	$ 15,039,146,000	$ 15,498,093,000		$ 14,363,638,000