Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 56,439	$ 50,868	$ 111,207	$ 100,844
Noninterest income	27,983	26,057	56,068	51,674
Income before taxes	33,628	26,401	66,821	51,600
Total Assets	7,046,589		7,046,589		$ 7,018,952
Operating Segments [Member] \| Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	17,832	15,699	36,352	31,542
Noninterest income	3,945	4,098	7,767	7,886
Income before taxes	11,784	10,240	24,858	19,588
Total Assets	2,506,852		2,506,852		2,493,096
Operating Segments [Member] \| Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	37,047	33,846	72,170	66,968
Noninterest income	13,660	14,408	26,937	28,004
Income before taxes	24,509	20,331	47,228	39,425
Total Assets	4,432,649		4,432,649		4,412,174
Operating Segments [Member] \| Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,698	1,591	3,193	3,007
Noninterest income	7,456	6,646	15,766	14,125
Income before taxes	3,119	2,431	6,764	5,545
Total Assets	97,894		97,894		83,594
Operating Segments [Member] \| Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(138)	(268)	(508)	(673)
Noninterest income	25,644	18,798	50,116	36,476
Income before taxes	16,720	11,247	32,231	21,747
Total Assets	824,524		824,524		803,810
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(22,722)	(17,893)	(44,518)	(34,817)
Income before taxes	(22,504)	$ (17,848)	(44,260)	$ (34,705)
Total Assets	$ (815,330)		$ (815,330)		$ (773,722)

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 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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