Investments (Amortized Cost and Estimated Fair Values of Investments Available-for-sale) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 639,668,000	$ 658,802,000
Gross Unrealized Gains	20,556,000	19,277,000
Gross Unrealized Losses	(2,515,000)	(5,870,000)
Estimated Fair Value	657,709,000us-gaap_AvailableForSaleSecurities	672,209,000us-gaap_AvailableForSaleSecurities
Marketable Equity Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	723,000	723,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	723,000	723,000
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	638,945,000	658,079,000
Gross Unrealized Gains	20,556,000	19,277,000
Gross Unrealized Losses	(2,515,000)	(5,870,000)
Estimated Fair Value	656,986,000	671,486,000
Debt Securities \| U.S. Government Agencies
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	144,519,000	144,497,000
Gross Unrealized Gains	253,000	0
Gross Unrealized Losses	(877,000)	(2,818,000)
Estimated Fair Value	143,895,000	141,679,000
Debt Securities \| State and municipal
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	155,964,000	157,603,000
Gross Unrealized Gains	9,822,000	9,453,000
Gross Unrealized Losses	0	(4,000)
Estimated Fair Value	165,786,000	167,052,000
Debt Securities \| Mortgage-Backed
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	337,351,000	354,631,000
Gross Unrealized Gains	10,481,000	9,824,000
Gross Unrealized Losses	(1,529,000)	(2,936,000)
Estimated Fair Value	346,303,000	361,519,000
Debt Securities \| Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	0	0
Debt Securities \| Trust Preferred
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,111,000	1,348,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(109,000)	(112,000)
Estimated Fair Value	$ 1,002,000	$ 1,236,000

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

-Publisher FASB

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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

-Publisher FASB

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

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