Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 46,876	$ 46,514	$ 138,717	$ 134,032
Noninterest income	25,324	24,938	79,335	72,111
Income before taxes	24,424	27,625	77,319	68,276
Total Assets	6,406,096		6,406,096		$ 6,574,972
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	15,221	15,267	45,946	44,426
Noninterest income	3,755	3,417	10,745	10,293
Income before taxes	9,463	10,640	29,152	25,914
Total Assets	2,220,378		2,220,378		2,298,828
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	30,429	30,076	88,928	86,272
Noninterest income	13,427	13,163	38,743	38,402
Income before taxes	18,693	21,377	52,500	54,146
Total Assets	4,081,832		4,081,832		4,113,783
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,638	1,594	5,156	4,538
Noninterest income	7,507	7,722	27,621	21,107
Income before taxes	3,098	3,002	15,015	8,360
Total Assets	124,713		124,713		145,814
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(412)	(423)	(1,313)	(1,204)
Noninterest income	17,250	20,105	55,868	51,979
Income before taxes	9,616	11,893	34,024	29,252
Total Assets	685,359		685,359		679,194
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(16,615)	(19,469)	(53,642)	(49,670)
Income before taxes	(16,446)	$ (19,287)	(53,372)	$ (49,396)
Total Assets	$ (706,186)		$ (706,186)		$ (662,647)