Investment Securities - Summary of Amortized Cost and Approximate Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 523,962	$ 568,550
Gross Unrealized Gains	13,031	1,773
Gross Unrealized Losses	(6,097)	(10,070)
Fair Value	530,896	560,253
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,930	39,925
Gross Unrealized Gains	1,111	320
Gross Unrealized Losses	0	(178)
Fair Value	46,041	40,067
Agency-guaranteed residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	251,755	299,392
Gross Unrealized Gains	2,890	1,453
Gross Unrealized Losses	(325)	(2,741)
Fair Value	254,320	298,104
Agency-guaranteed commercial real estate mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	204,769	206,719
Gross Unrealized Gains	9,030	0
Gross Unrealized Losses	0	(3,849)
Fair Value	213,799	202,870
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,508	22,514
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5,772)	(3,302)
Fair Value	$ 16,736	$ 19,212

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
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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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.

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-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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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