Investments (Amortized Cost and Estimated Fair Values of Investments Held-To-Maturity) (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 219,973,000	$ 224,638,000
Gross Unrealized Gains	4,346,000	1,949,000
Gross Unrealized Losses	(2,059,000)	(10,580,000)
Investments held-to-maturity, fair value	222,260,000	216,007,000
U.S. Government Agencies
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	64,512,000	64,505,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,734,000)	(4,827,000)
Investments held-to-maturity, fair value	62,778,000	59,678,000
State and municipal
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	155,261,000	159,889,000
Gross Unrealized Gains	4,321,000	1,920,000
Gross Unrealized Losses	(325,000)	(5,753,000)
Investments held-to-maturity, fair value	159,257,000	156,056,000
Mortgage-Backed
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	200,000	244,000
Gross Unrealized Gains	25,000	29,000
Gross Unrealized Losses	0	0
Investments held-to-maturity, fair value	$ 225,000	$ 273,000

Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

No definition available.

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- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

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Amount of unrecognized gain before loss on investments in held-to-maturity securities.

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Amount of unrecognized loss before gain on investments in held-to-maturity securities. Excludes write-down for other than temporary impairment (OTTI).

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