Other Comprehensive Income ((Loss) (Component of other comprehensive income (loss)) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Change in net unrealized gain/loss during the period	$ 40,122	$ 78,552	$ 62,972	$ 169,516
Reclassification adjustment for net (gains) losses included in net income		(6,409)	121	(6,414)
Total securities available for sale	40,122	72,143	63,093	163,102
Change in the net actuarial gain/loss	1,427	783	4,084	2,348
Change in the accumulated gain/loss on effective cash flow hedge derivatives	(269)	(909)	(760)	(2,560)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	(9,345)	(9,345)	(28,035)	(28,035)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Before Tax Amount	1,063	1,118	3,140	3,304
Total derivatives	(8,551)	(9,136)	(25,655)	(27,291)
Total other comprehensive income	32,998	63,790	41,522	138,159
Change in net unrealized gain/loss during the period	14,043	27,493	22,041	59,331
Reclassification adjustment for net (gains) losses included in net income		(2,243)	42	(2,245)
Total securities available for sale	14,043	25,250	22,083	57,086
Change in the net actuarial gain/loss	499	274	1,429	822
Change in the accumulated gain/loss on effective cash flow hedge derivatives	(93)	(318)	(266)	(896)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)	(3,271)	(3,271)	(9,812)	(9,812)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Tax Expense (Benefit)	372	391	1,099	1,156
Total derivatives	(2,992)	(3,198)	(8,979)	(9,552)
Total other comprehensive income	11,550	22,326	14,533	48,356
Change in net unrealized gain/loss during the period	26,079	51,059	40,931	110,185
Reclassification adjustment for net (gains) losses included in net income		(4,166)	79	(4,169)
Total securities available for sale	26,079	46,893	41,010	106,016
Change in the net actuarial gain/loss	928	509	2,655	1,526
Change in the accumulated gain/loss on effective cash flow hedge derivatives	(176)	(591)	(494)	(1,664)
Interest rate swaps on variable-rate loans	(6,074)	(6,074)	(18,223)	(18,223)
Interest rate swap on junior subordinated deferrable interest debentures	691	727	2,041	2,148
Total derivatives	(5,559)	(5,938)	(16,676)	(17,739)
Other comprehensive income (loss), net of tax	$ 21,448	$ 41,464	$ 26,989	$ 89,803