Segment Reporting (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (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]
Interest income	$ 40,317	$ 37,150	$ 117,238	$ 110,391
Interest expense	5,201	4,730	14,816	14,070
Provision (credit) for loan and lease losses	1,706	(192)	3,521	(1,016)
Non-interest income	12,390	12,590	37,658	35,533
Non-interest Expense	29,630	28,632	88,351	90,322
Income before income taxes	16,170	16,570	48,208	42,548
Income tax expense	5,175	5,428	15,655	13,496
Net income	10,995	11,142	32,553	29,052
Assets	4,611,034	4,248,731	4,611,034	4,248,731	$ 4,397,132
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(2)	(2)	(5)	(16)
Interest expense	(2)	(2)	(5)	(16)
Provision (credit) for loan and lease losses	0	0	0	0
Non-interest income	(181)	(175)	(15,936)	(3,526)
Non-interest Expense	(181)	(175)	(15,936)	(3,526)
Income before income taxes	0	0	0	0
Income tax expense	0	0	0	0
Net income	0	0	0	0
Assets	(18,302)	(18,834)	(18,302)	(18,834)
Community Banking
Segment Reporting Information [Line Items]
Interest income	40,318	37,150	117,238	110,391
Interest expense	5,203	4,732	14,821	14,086
Provision (credit) for loan and lease losses	1,706	(192)	3,521	(1,016)
Non-interest income	9,106	9,545	43,887	29,669
Non-interest Expense	27,318	26,632	97,294	87,550
Income before income taxes	15,197	15,523	45,489	39,440
Income tax expense	4,786	5,014	14,583	12,272
Net income	10,411	10,509	30,906	27,168
Assets	4,612,413	4,250,103	4,612,413	4,250,103
Insurance
Segment Reporting Information [Line Items]
Interest income	0	1	1	6
Interest expense	0	0	0	0
Provision (credit) for loan and lease losses	0	0	0	0
Non-interest income	1,716	1,498	4,394	4,273
Non-interest Expense	1,480	1,226	4,032	3,542
Income before income taxes	236	273	363	737
Income tax expense	101	110	153	298
Net income	135	163	210	439
Assets	5,788	6,053	5,788	6,053
Investment Management
Segment Reporting Information [Line Items]
Interest income	1	1	4	10
Interest expense	0	0	0	0
Provision (credit) for loan and lease losses	0	0	0	0
Non-interest income	1,749	1,722	5,313	5,117
Non-interest Expense	1,013	949	2,961	2,756
Income before income taxes	737	774	2,356	2,371
Income tax expense	288	304	919	926
Net income	449	470	1,437	1,445
Assets	$ 11,135	$ 11,409	$ 11,135	$ 11,409