Supplemental Comprehensive Income Disclosures - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income [Line Items]
Unrealized holding (losses) gains on securities arising during the period, Pretax Amount	$ (44,767)	$ (2,854)	$ 9,727
Noncredit related gains (losses) on securities not expected to be sold, Pretax Amount	9,792	2,193	(425)
Less: reclassification adjustment for (gains) losses on securities included in net income, Pretax Amount	1,158	(192)	(2,185)
Total Unrealized (Losses) Gains on Securities, before Tax	(33,817)	(853)	7,117
Transition obligation	0	2	2
Net (loss) gain, Pretax Amount	219	(300)	(260)
Total Unrealized Gains (Losses) for Postretirement Obligations, Before Tax	219	(298)	(258)
Total other comprehensive (loss) income, Pretax Amount	(33,598)	(1,151)	6,859
Unrealized holding (losses) gains on securities arising during the period, Tax (Expense) Benefit	15,660	1,006	(3,404)
Noncredit related gains (losses) on securities not expected to be sold, Tax (Expense) Benefit	(3,427)	(768)	149
Less: reclassification adjustment for (gains) losses on securities included in net income, Tax (Expense) Benefit	(405)	67	765
Total Unrealized (Losses) Gains on Securities, Tax (Expense) Benefit	11,828	305	(2,490)
Transition obligation, Tax (Expense) Benefit	0	(1)	(1)
Net (loss) gain, Tax (Expense) Benefit	(77)	105	91
Total Unrealized Gains (Losses) for Postretirement Obligations, Tax (Expense) Benefit	(77)	104	90
Total other comprehensive (loss) income, Tax (Expense) Benefit	11,751	409	(2,400)
Unrealized holding (losses) gains on securities arising during the period, Net of Tax Amount	(29,107)	(1,848)	6,323
Noncredit related gains (losses) on securities not expected to be sold, Net of Tax Amount	6,365	1,425	(276)
Less: reclassification adjustment for (gains) losses on securities included in net income, Net of Tax Amount	753	(125)	(1,420)
Total Unrealized (Losses) Gains on Securities, Net of Tax	(21,989)	(548)	4,627
Transition obligation, Net of Tax Amount	0	1	1
Net (loss) gain, Net of Tax Amount	142	(195)	(169)
Total Unrealized Gains (Losses) for Postretirement Obligations, Net of Tax	142	(194)	(168)
Total other comprehensive (loss) Income	$ (21,847)	$ (742)	$ 4,459