Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 57,233	$ 51,431	$ 168,440	$ 152,275
Noninterest income	29,169	27,927	85,237	79,601
Income before taxes	32,526	27,214	99,347	78,814
Total Assets	7,132,168		7,132,168		$ 7,018,952
Operating Segments [Member] \| Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	18,617	15,893	54,969	47,435
Noninterest income	3,981	4,235	11,748	12,121
Income before taxes	11,499	10,970	36,357	30,558
Total Assets	2,549,122		2,549,122		2,493,096
Operating Segments [Member] \| Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	37,310	34,254	109,480	101,222
Noninterest income	13,884	14,918	40,821	42,922
Income before taxes	23,810	19,727	71,038	59,152
Total Assets	4,449,130		4,449,130		4,412,174
Operating Segments [Member] \| Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,332	1,617	4,525	4,624
Noninterest income	9,217	8,050	24,983	22,175
Income before taxes	3,762	2,683	10,526	8,228
Total Assets	92,387		92,387		83,594
Operating Segments [Member] \| Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(26)	(333)	(534)	(1,006)
Noninterest income	24,470	19,025	74,586	55,501
Income before taxes	15,137	11,964	47,368	33,711
Total Assets	873,337		873,337		803,810
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(22,383)	(18,301)	(66,901)	(53,118)
Income before taxes	(21,682)	$ (18,130)	(65,942)	$ (52,835)
Total Assets	$ (831,808)		$ (831,808)		$ (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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