Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 50,868	$ 46,215	$ 100,844	$ 91,841
Noninterest income	26,057	28,715	51,674	54,011
Income before taxes	26,401	28,230	51,600	52,895
Total Assets	6,683,376		6,683,376		$ 6,692,829
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	15,699	15,325	31,542	30,725
Noninterest income	4,098	3,533	7,886	6,990
Income before taxes	10,240	9,800	19,588	19,689
Total Assets	2,311,639		2,311,639		2,277,870
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	33,846	29,444	66,968	58,499
Noninterest income	14,408	12,990	28,004	25,316
Income before taxes	20,331	17,400	39,425	33,807
Total Assets	4,350,115		4,350,115		4,379,205
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,591	1,900	3,007	3,518
Noninterest income	6,646	11,387	14,125	20,114
Income before taxes	2,431	6,910	5,545	11,917
Total Assets	107,265		107,265		128,697
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(268)	(454)	(673)	(901)
Noninterest income	18,798	21,326	36,476	38,618
Income before taxes	11,247	14,604	21,747	24,408
Total Assets	653,042		653,042		624,428
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(17,893)	(20,521)	(34,817)	(37,027)
Income before taxes	(17,848)	$ (20,484)	(34,705)	$ (36,926)
Total Assets	$ (738,685)		$ (738,685)		$ (717,371)