INVESTMENTS (Gross Unrealized Losses and Fair Value by Length of Time of Available-For-Sale Securities) (Detail) $ in Thousands	Jun. 30, 2018 USD ($) Securities	Dec. 31, 2017 USD ($) Securities
Schedule Of Available For Sale Securities [Line Items]
Number of Securities \| Securities	317	79
Fair Value	$ 696,361	$ 346,417
Less than 12 months	9,738	1,054
More than 12 months	10,346	6,105
Total Unrealized Losses	$ 20,084	$ 7,159
Us Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities \| Securities	57	13
Fair Value	$ 206,448	$ 106,568
Less than 12 months	2,893	545
More than 12 months	3,496	2,236
Total Unrealized Losses	$ 6,389	$ 2,781
U S States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities \| Securities	117	20
Fair Value	$ 112,777	$ 18,228
Less than 12 months	1,889	107
More than 12 months	41	62
Total Unrealized Losses	$ 1,930	$ 169
Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities \| Securities	143	46
Fair Value	$ 377,136	$ 221,621
Less than 12 months	4,956	402
More than 12 months	6,809	3,807
Total Unrealized Losses	$ 11,765	$ 4,209
Trust Preferred Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of Securities \| Securities	0	0
Fair Value	$ 0	$ 0
Less than 12 months	0	0
More than 12 months	0	0
Total Unrealized Losses	$ 0	$ 0

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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