Segment Reporting (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Interest income	$ 38,849	$ 36,991	$ 76,921	$ 73,241
Interest expense	4,916	4,682	9,615	9,340
Provision (credit) for loan and lease losses	1,218	158	1,815	(824)
Non-interest income	12,109	11,694	25,268	22,943
Non-interest Expense	29,477	34,141	58,721	61,690
Income before income taxes	15,347	9,704	32,038	25,978
Income tax expense	5,014	2,722	10,480	8,068
Net income	10,333	6,982	21,558	17,910
Assets	4,507,367	4,234,342	4,507,367	4,234,342	$ 4,397,132
Community Banking
Segment Reporting Information [Line Items]
Interest income	38,849	36,991	76,920	73,241
Interest expense	4,918	4,690	9,618	9,354
Provision (credit) for loan and lease losses	1,218	158	1,815	(824)
Non-interest income	24,945	12,108	34,781	20,123
Non-interest Expense	42,958	35,305	69,975	60,917
Income before income taxes	14,700	8,946	30,293	23,917
Income tax expense	4,763	2,427	9,797	7,258
Net income	9,937	6,519	20,496	16,659
Assets	4,508,858	4,257,129	4,508,858	4,257,129
Insurance
Segment Reporting Information [Line Items]
Interest income	0	3	1	5
Interest expense	0	0	0	0
Provision (credit) for loan and lease losses	0	0	0	0
Non-interest income	984	1,045	2,678	2,776
Non-interest Expense	1,169	1,125	2,552	2,317
Income before income taxes	(185)	(77)	127	464
Income tax expense	(74)	(30)	52	188
Net income	(111)	(47)	75	276
Assets	5,647	6,025	5,647	6,025
Investment Management
Segment Reporting Information [Line Items]
Interest income	2	5	3	9
Interest expense	0	0	0	0
Provision (credit) for loan and lease losses	0	0	0	0
Non-interest income	1,754	1,717	3,564	3,395
Non-interest Expense	924	887	1,949	1,807
Income before income taxes	832	835	1,618	1,597
Income tax expense	325	325	631	622
Net income	507	510	987	975
Assets	10,672	10,927	10,672	10,927
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(2)	(8)	(3)	(14)
Interest expense	(2)	(8)	(3)	(14)
Provision (credit) for loan and lease losses	0	0	0	0
Non-interest income	(15,574)	(3,176)	(15,755)	(3,351)
Non-interest Expense	(15,574)	(3,176)	(15,755)	(3,351)
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Assets	$ (17,810)	$ (39,739)	$ (17,810)	$ (39,739)