Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 51,431	$ 46,876	$ 152,275	$ 138,717
Noninterest income	27,927	25,324	79,601	79,335
Income before taxes	27,214	24,424	78,814	77,319
Total Assets	6,783,537		6,783,537		$ 6,692,829
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	15,893	15,221	47,435	45,946
Noninterest income	4,235	3,755	12,121	10,745
Income before taxes	10,970	9,463	30,558	29,152
Total Assets	2,351,771		2,351,771		2,277,870
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	34,254	30,429	101,222	88,928
Noninterest income	14,918	13,427	42,922	38,743
Income before taxes	19,727	18,693	59,152	52,500
Total Assets	4,360,964		4,360,964		4,379,205
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,617	1,638	4,624	5,156
Noninterest income	8,050	7,507	22,175	27,621
Income before taxes	2,683	3,098	8,228	15,015
Total Assets	95,999		95,999		128,697
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(333)	(412)	(1,006)	(1,313)
Noninterest income	19,025	17,250	55,501	55,868
Income before taxes	11,964	9,616	33,711	34,024
Total Assets	733,573		733,573		624,428
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(18,301)	(16,615)	(53,118)	(53,642)
Income before taxes	(18,130)	$ (16,446)	(52,835)	$ (53,372)
Total Assets	$ (758,770)		$ (758,770)		$ (717,371)