Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning Balance	$ (25,021)	$ 22,342	$ 29,801	$ 15,004
Other comprehensive income (loss) before reclassifications	(20,324)	13,112	(73,888)	23,776
Amounts reclassified from accumulated other comprehensive income (loss)	415	(1,174)	(843)	(4,500)
Net current-period other comprehensive income (loss)	(19,909)	11,938	(74,731)	19,276
AOCI, Ending Balance	(44,930)	34,280	(44,930)	34,280
Accumulated Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning Balance	(16,773)	31,163	39,054	24,612
Other comprehensive income (loss) before reclassifications	1,500	14,064	(52,589)	24,728
Amounts reclassified from accumulated other comprehensive income (loss)	(248)	(1,638)	(1,986)	(5,751)
Net current-period other comprehensive income (loss)	1,252	12,426	(54,575)	18,977
AOCI, Ending Balance	(15,521)	43,589	(15,521)	43,589
Accumulated Unrealized Gains Losses on Held-to-Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning Balance	3,056	4,468	3,269	4,745
Other comprehensive income (loss) before reclassifications	(20,224)	(952)	(20,224)	(952)
Amounts reclassified from accumulated other comprehensive income (loss)	137	(139)	(76)	(416)
Net current-period other comprehensive income (loss)	(20,087)	(1,091)	(20,300)	(1,368)
AOCI, Ending Balance	(17,031)	3,377	(17,031)	3,377
Accumulated Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning Balance	525	1		145
Other comprehensive income (loss) before reclassifications	(1,600)		(1,075)
Amounts reclassified from accumulated other comprehensive income (loss)		(1)		(145)
Net current-period other comprehensive income (loss)	(1,600)	(1)	(1,075)	(145)
AOCI, Ending Balance	(1,075)		(1,075)
Accumulated Defined Benefit Pensions Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Beginning Balance	(11,829)	(13,290)	(12,522)	(14,498)
Amounts reclassified from accumulated other comprehensive income (loss)	526	604	1,219	1,812
Net current-period other comprehensive income (loss)	526	604	1,219	1,812
AOCI, Ending Balance	$ (11,303)	$ (12,686)	$ (11,303)	$ (12,686)