Segment Reporting (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Interest income	$ 37,150	$ 40,180	$ 110,391	$ 112,238
Interest expense	4,730	4,874	14,070	14,674
Provision (credit) for loan and lease losses	(192)	1,128	(1,016)	(1,670)
Noninterest income	12,590	11,223	35,533	35,857
Noninterest expenses	28,632	26,893	90,322	82,224
Income before income taxes	16,570	18,508	42,548	52,867
Income tax expense	5,428	6,419	13,496	18,058
Net income	11,142	12,089	29,052	34,809
Assets	4,248,731	4,052,969	4,248,731	4,052,969	4,106,100
Community Banking
Segment Reporting Information [Line Items]
Interest income	37,150	40,180	110,391	112,238
Interest expense	4,732	4,879	14,086	14,691
Provision (credit) for loan and lease losses	(192)	1,128	(1,016)	(1,670)
Noninterest income	9,545	8,453	29,669	27,748
Noninterest expenses	26,632	24,939	87,550	76,893
Income before income taxes	15,523	17,687	39,440	50,072
Income tax expense	5,014	6,094	12,272	16,955
Net income	10,509	11,593	27,168	33,117
Assets	4,250,103	4,088,617	4,250,103	4,088,617
Insurance
Segment Reporting Information [Line Items]
Interest income	1	1	6	6
Noninterest income	1,498	1,271	4,273	3,968
Noninterest expenses	1,226	1,135	3,542	3,270
Income before income taxes	273	137	737	704
Income tax expense	110	55	298	285
Net income	163	82	439	419
Assets	6,053	13,907	6,053	13,907
Investment Management
Segment Reporting Information [Line Items]
Interest income	1	4	10	11
Noninterest income	1,722	1,573	5,117	4,622
Noninterest expenses	949	893	2,756	2,542
Income before income taxes	774	684	2,371	2,091
Income tax expense	304	270	926	818
Net income	470	414	1,445	1,273
Assets	11,409	18,350	11,409	18,350
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(2)	(5)	(16)	(17)
Interest expense	(2)	(5)	(16)	(17)
Noninterest income	(175)	(74)	(3,526)	(481)
Noninterest expenses	(175)	(74)	(3,526)	(481)
Assets	$ (18,834)	$ (67,905)	$ (18,834)	$ (67,905)