Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Detail) $ in Thousands	Sep. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	2	23
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 7,912	$ 213,997
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (8)	$ (1,302)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	3
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 24,014
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ (414)
Available-for-sale, Securities, Number of Positions \| security	2	26
Available-for-sale Securities, Fair Value, Total	$ 7,912	$ 238,011
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (8)	$ (1,716)
US Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	0
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 0
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	0	0
Available-for-sale Securities, Fair Value, Total	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ 0
Obligations of U.S. Government Corporations and Agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	10
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 88,584
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ (379)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	2
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 14,542
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ (188)
Available-for-sale, Securities, Number of Positions \| security	0	12
Available-for-sale Securities, Fair Value, Total	$ 0	$ 103,126
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ (567)
Collateralized Mortgage Obligations of U.S. Government Corporations and Agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	6
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 61,211
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ (316)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	0	6
Available-for-sale Securities, Fair Value, Total	$ 0	$ 61,211
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ (316)
Residential Mortgage-Backed Securities of U.S. Government Corporations and Agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 7,993
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ (151)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	0	1
Available-for-sale Securities, Fair Value, Total	$ 0	$ 7,993
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ (151)
Commercial Mortgage-Backed Securities of U.S. Government Corporations and Agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	1	5
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 7,841	$ 50,839
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (8)	$ (450)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	1
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 9,472
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ (226)
Available-for-sale, Securities, Number of Positions \| security	1	6
Available-for-sale Securities, Fair Value, Total	$ 7,841	$ 60,311
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (8)	$ (676)
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 5,370
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ (6)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	0	1
Available-for-sale Securities, Fair Value, Total	$ 0	$ 5,370
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ (6)
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	1	23
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 7,841	$ 213,997
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (8)	$ (1,302)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	3
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 24,014
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ (414)
Available-for-sale, Securities, Number of Positions \| security	1	26
Available-for-sale Securities, Fair Value, Total	$ 7,841	$ 238,011
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (8)	$ (1,716)
Marketable Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 71
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0
Available-for-sale, Securities, Number of Positions \| security	1	0
Available-for-sale Securities, Fair Value, Total	$ 71
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 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=73527792&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=73527792&loc=d3e27337-111563

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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