Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	$ 54,120		$ 45,032
Without a related allowance, Unpaid Principal Balance	66,949		50,286
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	6,082		618
With a related allowance recorded, Unpaid Principal Balance	7,438		1,468
Impaired Financing Receivable, Recorded Investment	60,202		45,650
Impaired Financing Receivable, Unpaid Principal Balance, Total	74,387		51,754
Impaired Financing Receivable, Related Allowance	2,213		37
Without a related allowance recorded, Average Recorded Investment	56,028	$ 48,285
Without a related allowance recorded, Interest Income Recognized	547	375
With a related allowance recorded, Average Recorded Investment	6,616	884
With a related allowance recorded, Interest Income Recognized	40	9
Impaired Financing Receivable, Average Recorded Investment, Total	62,644	49,169
Impaired Financing Receivable, Interest Income Recognized, Total	587	384
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	18,505		12,661
Without a related allowance, Unpaid Principal Balance	26,493		13,157
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	0		0
With a related allowance recorded, Unpaid Principal Balance	0		0
Impaired Financing Receivable, Recorded Investment	18,505		12,661
Impaired Financing Receivable, Unpaid Principal Balance, Total	26,493		13,157
Impaired Financing Receivable, Related Allowance	0		0
Without a related allowance recorded, Average Recorded Investment	18,605	22,627
Without a related allowance recorded, Interest Income Recognized	199	164
With a related allowance recorded, Average Recorded Investment	0	823
With a related allowance recorded, Interest Income Recognized	0	8
Impaired Financing Receivable, Average Recorded Investment, Total	18,605	23,450
Impaired Financing Receivable, Interest Income Recognized, Total	199	172
Commercial and Industrial
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	13,778		14,417
Without a related allowance, Unpaid Principal Balance	14,750		15,220
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	4,850		0
With a related allowance recorded, Unpaid Principal Balance	5,356		0
Impaired Financing Receivable, Recorded Investment	18,628		14,417
Impaired Financing Receivable, Unpaid Principal Balance, Total	20,106		15,220
Impaired Financing Receivable, Related Allowance	2,027		0
Without a related allowance recorded, Average Recorded Investment	15,513	10,847
Without a related allowance recorded, Interest Income Recognized	149	62
With a related allowance recorded, Average Recorded Investment	5,382	0
With a related allowance recorded, Interest Income Recognized	32	0
Impaired Financing Receivable, Average Recorded Investment, Total	20,895	10,847
Impaired Financing Receivable, Interest Income Recognized, Total	181	62
Commercial Construction
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	10,772		10,998
Without a related allowance, Unpaid Principal Balance	13,974		14,200
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	1,116		500
With a related allowance recorded, Unpaid Principal Balance	1,966		1,350
Impaired Financing Receivable, Recorded Investment	11,888		11,498
Impaired Financing Receivable, Unpaid Principal Balance, Total	15,940		15,550
Impaired Financing Receivable, Related Allowance	154		3
Without a related allowance recorded, Average Recorded Investment	10,782	7,704
Without a related allowance recorded, Interest Income Recognized	64	53
With a related allowance recorded, Average Recorded Investment	1,117	0
With a related allowance recorded, Interest Income Recognized	6	0
Impaired Financing Receivable, Average Recorded Investment, Total	11,899	7,704
Impaired Financing Receivable, Interest Income Recognized, Total	70	53
Consumer Real Estate
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	11,038		6,845
Without a related allowance, Unpaid Principal Balance	11,703		7,521
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	114		116
With a related allowance recorded, Unpaid Principal Balance	114		116
Impaired Financing Receivable, Recorded Investment	11,152		6,961
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,817		7,637
Impaired Financing Receivable, Related Allowance	30		32
Without a related allowance recorded, Average Recorded Investment	11,102	7,073
Without a related allowance recorded, Interest Income Recognized	135	96
With a related allowance recorded, Average Recorded Investment	115	42
With a related allowance recorded, Interest Income Recognized	2	1
Impaired Financing Receivable, Average Recorded Investment, Total	11,217	7,115
Impaired Financing Receivable, Interest Income Recognized, Total	137	97
Other Consumer
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	27		111
Without a related allowance, Unpaid Principal Balance	29		188
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	2		2
With a related allowance recorded, Unpaid Principal Balance	2		2
Impaired Financing Receivable, Recorded Investment	29		113
Impaired Financing Receivable, Unpaid Principal Balance, Total	31		190
Impaired Financing Receivable, Related Allowance	2		$ 2
Without a related allowance recorded, Average Recorded Investment	26	34
Without a related allowance recorded, Interest Income Recognized	0	0
With a related allowance recorded, Average Recorded Investment	2	19
With a related allowance recorded, Interest Income Recognized	0	0
Impaired Financing Receivable, Average Recorded Investment, Total	28	53
Impaired Financing Receivable, Interest Income Recognized, Total	$ 0	$ 0

Impaired financing receivable with no related allowance.

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- Definition

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+ References

No definition available.

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

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- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

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Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

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Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

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