Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 54,768	$ 49,976
Noninterest income	28,085	25,617
Income before taxes	33,193	25,199
Total Assets	7,189,637		$ 7,018,952
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	18,520	15,843
Noninterest income	3,822	3,788
Income before taxes	13,074	9,348
Total Assets	2,569,703		2,493,096
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	35,123	33,122
Noninterest income	13,277	13,596
Income before taxes	22,719	19,094
Total Assets	4,481,943		4,412,174
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,495	1,416
Noninterest income	8,310	7,479
Income before taxes	3,645	3,114
Total Assets	75,587		83,594
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(370)	(405)
Noninterest income	24,472	17,678
Income before taxes	15,511	10,500
Total Assets	854,316		803,810
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(21,796)	(16,924)
Income before taxes	(21,756)	$ (16,857)
Total Assets	$ (791,912)		$ (773,722)