Segment Information - Results of Operations and Selected Financial Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 45,626us-gaap_InterestIncomeExpenseNet	$ 42,029us-gaap_InterestIncomeExpenseNet
Noninterest income	25,296us-gaap_NoninterestIncome	23,562us-gaap_NoninterestIncome
Income before taxes	24,665	20,537
Total Assets	6,570,120us-gaap_Assets	6,375,041us-gaap_Assets	6,574,972us-gaap_Assets
Operating Segments [Member] \| Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	15,400	13,787
Noninterest income	3,457	3,413
Income before taxes	9,889	7,790
Total Assets	2,299,513	2,093,563	2,298,828
Operating Segments [Member] \| Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	29,055	27,241
Noninterest income	12,326	12,266
Income before taxes	16,407	15,077
Total Assets	4,162,565	3,973,407	4,113,783
Operating Segments [Member] \| Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,618	1,376
Noninterest income	8,727	7,056
Income before taxes	5,007	3,066
Total Assets	133,236	113,732	145,814
Operating Segments [Member] \| Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(447)	(375)
Noninterest income	17,292	15,955
Income before taxes	9,804	9,679
Total Assets	651,810	816,489	679,194
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(16,506)	(15,128)
Income before taxes	(16,442)	(15,075)
Total Assets	$ (677,004)	$ (622,150)	$ (662,647)

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.18)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Section S99

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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-Name Regulation S-X (SX)

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- Definition

Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h)(1)(i))

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- Definition

The net amount of operating interest income (expense).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.10)

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

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The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

+ References

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

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-Name Accounting Standards Codification

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