Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 46,215	$ 45,489	$ 91,841	$ 87,518
Noninterest income	28,715	23,611	54,011	47,173
Income before taxes	28,230	20,114	52,895	40,651
Total Assets	6,498,898		6,498,898		$ 6,574,972
Operating Segments [Member] \| Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	15,325	15,372	30,725	29,159
Noninterest income	3,533	3,463	6,990	6,876
Income before taxes	9,800	7,484	19,689	15,274
Total Assets	2,262,905		2,262,905		2,298,828
Operating Segments [Member] \| Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	29,444	28,955	58,499	56,196
Noninterest income	12,990	12,973	25,316	25,239
Income before taxes	17,400	17,692	33,807	32,769
Total Assets	4,093,820		4,093,820		4,113,783
Operating Segments [Member] \| Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,900	1,568	3,518	2,944
Noninterest income	11,387	6,329	20,114	13,385
Income before taxes	6,910	2,292	11,917	5,358
Total Assets	170,089		170,089		145,814
Operating Segments [Member] \| Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(454)	(406)	(901)	(781)
Noninterest income	21,326	15,919	38,618	31,874
Income before taxes	14,604	7,680	24,408	17,359
Total Assets	667,250		667,250		679,194
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(20,521)	(15,073)	(37,027)	(30,201)
Income before taxes	(20,484)	$ (15,034)	(36,926)	$ (30,109)
Total Assets	$ (695,166)		$ (695,166)		$ (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

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

-Publisher SEC

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

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The net amount of operating interest income (expense).

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