Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net interest income	$ 68,792	$ 64,880	$ 135,695	$ 127,915
Noninterest income	34,077	30,437	66,078	60,547
Income before taxes	43,828	39,836	84,842	76,777
Total Assets	7,642,021		7,642,021		$ 7,574,258
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	21,438	21,084	42,791	41,388
Noninterest income	4,635	4,184	8,844	8,125
Income before taxes	14,866	14,883	30,235	29,619
Total Assets	2,795,525		2,795,525		2,743,876
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	44,775	42,068	88,182	83,450
Noninterest income	16,243	14,832	31,128	28,785
Income before taxes	30,041	27,942	58,086	54,290
Total Assets	4,981,139		4,981,139		4,892,946
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income	1,411	1,358	2,582	2,833
Noninterest income	10,105	8,896	19,978	18,520
Income before taxes	5,572	4,028	10,071	9,071
Total Assets	45,972		45,972		84,706
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income	1,168	370	2,140	244
Noninterest income	37,917	33,609	73,438	65,803
Income before taxes	27,590	23,622	52,613	43,537
Total Assets	883,471		883,471		861,782
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(34,823)	(31,084)	(67,310)	(60,686)
Income before taxes	(34,241)	$ (30,639)	(66,163)	$ (59,740)
Total Assets	$ (1,064,086)		$ (1,064,086)		$ (1,009,052)