Investments (Amortized Cost and Estimated Fair Values of Investments Held-To-Maturity) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 217,557,000	$ 219,973,000
Gross Unrealized Gains	5,011,000	4,346,000
Gross Unrealized Losses	(881,000)	(2,059,000)
Investments held-to-maturity, fair value	221,687,000	222,260,000
U.S. Government Agencies
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	64,514,000	64,512,000
Gross Unrealized Gains	13,000	0
Gross Unrealized Losses	(697,000)	(1,734,000)
Investments held-to-maturity, fair value	63,830,000	62,778,000
State and municipal
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	152,849,000	155,261,000
Gross Unrealized Gains	4,968,000	4,321,000
Gross Unrealized Losses	(184,000)	(325,000)
Investments held-to-maturity, fair value	157,633,000	159,257,000
Mortgage-Backed
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	194,000	200,000
Gross Unrealized Gains	30,000	25,000
Gross Unrealized Losses	0	0
Investments held-to-maturity, fair value	$ 224,000	$ 225,000

Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

+ References

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

+ References

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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

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-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

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