Fair Values of Assets and Liabilities - Schedule of Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	$ 23,212	$ 28,554		$ 37,812	$ 49,641
Total gains or losses included in earnings	0	(4,520)		2,409	(4,129)
Total gains or losses included in other comprehensive income	2,030	(2,211)		3,610	691
Purchases	0	0		0	0
Issuances	0	0		0	0
Sales	0	0		(15,981)	(7,027)
Settlements	(771)	(75)		(3,840)	(5,463)
Transfers from Level 3	0	4,520	(12,000)		(11,965)
Transfers into Level 3	0			461	4,520
Balance, end of period	24,471	26,268	28,554	24,471	26,268
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	21,792	26,984		22,980	26,352
Total gains or losses included in earnings	0	0		0	0
Total gains or losses included in other comprehensive income	2,030	(2,211)		3,610	809
Purchases	0	0		0	0
Issuances	0	0		0	0
Sales	0	0		0	0
Settlements	(771)	(75)		(3,539)	(2,463)
Transfers from Level 3	0	0			0
Transfers into Level 3	0			0	0
Balance, end of period	23,051	24,698		23,051	24,698
Equities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	1,420	1,570		1,420	1,570
Total gains or losses included in earnings	0	0		0	0
Total gains or losses included in other comprehensive income	0	0		0	0
Purchases	0	0		0	0
Issuances	0	0		0	0
Sales	0	0		0	0
Settlements	0	0		0	0
Transfers from Level 3	0	0			0
Transfers into Level 3	0			0	0
Balance, end of period	1,420	1,570		1,420	1,570
Loans Held for Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	0			13,412
Total gains or losses included in earnings	0			2,870
Total gains or losses included in other comprehensive income	0			0
Purchases	0			0
Issuances	0			0
Sales	0			(15,981)
Settlements	0			(301)
Transfers from Level 3	0
Transfers into Level 3	0			0
Balance, end of period	0			0
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	0	0		0	0
Total gains or losses included in earnings	0	(4,520)		(461)	(4,520)
Total gains or losses included in other comprehensive income	0	0		0	0
Purchases	0	0		0	0
Issuances	0	0		0	0
Sales	0	0		0	0
Settlements	0	0		0	0
Transfers from Level 3	0	4,520			0
Transfers into Level 3	0			461	4,520
Balance, end of period	0	0		0	0
Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period		0			343
Total gains or losses included in earnings		0			4
Total gains or losses included in other comprehensive income		0			(20)
Purchases		0			0
Issuances		0			0
Sales		0			(327)
Settlements		0			0
Transfers from Level 3		0			0
Transfers into Level 3					0
Balance, end of period		0			0
Corporate securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period		0			21,376
Total gains or losses included in earnings		0			387
Total gains or losses included in other comprehensive income		0			(98)
Purchases		0			0
Issuances		0			0
Sales		0			(6,700)
Settlements		0			(3,000)
Transfers from Level 3		0			(11,965)
Transfers into Level 3					0
Balance, end of period		$ 0			$ 0