Segment Reporting (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Interest income	$ 41,074	$ 40,317	$ 38,849	$ 38,072	$ 37,975	$ 37,150	$ 36,991	$ 36,250	$ 158,312	$ 148,366	$ 149,347
Interest expense	5,297	5,201	4,916	4,699	4,748	4,730	4,682	4,658	20,113	18,818	19,433
Provision (credit)	1,850	1,706	1,218	597	853	(192)	158	(982)	5,371	(163)	(1,084)
Non-interest income	12,243	12,390	12,109	13,159	11,338	12,590	11,694	11,249	49,901	46,871	47,511
Non-interest Expense	26,996	29,630	29,477	29,244	30,478	28,632	34,141	27,549	115,347	120,800	111,524
Income before income taxes	19,174	16,170	15,347	16,691	13,234	16,570	9,704	16,274	67,382	55,782	66,985
Income tax expense	6,372	5,175	5,014	5,466	4,086	5,428	2,722	5,346	22,027	17,582	22,563
Net income	12,802	$ 10,995	$ 10,333	$ 11,225	9,148	$ 11,142	$ 6,982	$ 10,928	45,355	38,200	44,422
Assets	4,655,380				4,397,132				4,655,380	4,397,132	4,106,100
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income									(6)	(17)	(25)
Interest expense									(6)	(17)	(25)
Provision (credit)									0	0	0
Non-interest income									(16,117)	(3,701)	(641)
Non-interest Expense									(16,117)	(3,701)	(641)
Income before income taxes									0	0	0
Income tax expense									0	0	0
Net income									0	0	0
Assets	(19,393)				(19,756)				(19,393)	(19,756)	(69,390)
Community Banking
Segment Reporting Information [Line Items]
Interest income									158,313	148,366	149,347
Interest expense									20,119	18,835	19,458
Provision (credit)									5,371	(163)	(1,084)
Non-interest income									53,398	38,388	36,588
Non-interest Expense									122,183	115,577	104,392
Income before income taxes									64,038	52,505	63,169
Income tax expense									20,710	16,300	21,060
Net income									43,328	36,205	42,109
Assets	4,656,573				4,399,133				4,656,573	4,399,133	4,143,368
Insurance
Segment Reporting Information [Line Items]
Interest income									1	6	9
Interest expense									0	0	0
Provision (credit)									0	0	0
Non-interest income									5,516	5,386	5,280
Non-interest Expense									5,189	5,290	4,392
Income before income taxes									328	102	897
Income tax expense									141	43	363
Net income									187	59	534
Assets	5,542				5,842				5,542	5,842	13,990
Investment Management
Segment Reporting Information [Line Items]
Interest income									4	11	16
Interest expense									0	0	0
Provision (credit)									0	0	0
Non-interest income									7,104	6,798	6,284
Non-interest Expense									4,092	3,634	3,381
Income before income taxes									3,016	3,175	2,919
Income tax expense									1,176	1,239	1,140
Net income									1,840	1,936	1,779
Assets	$ 12,658				$ 11,913				$ 12,658	$ 11,913	$ 18,132