Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Interest income	$ 35,558	$ 35,008	$ 70,173	$ 69,758
Interest expense	5,749	6,854	11,659	13,594
Provision for loan and lease losses	1,585	1,151	2,249	2,666	1,428
Noninterest income	11,493	10,802	22,467	20,794
Noninterest expenses	28,858	25,838	55,541	51,900
Income before income taxes	10,859	11,967	23,191	22,392
Income tax expense	3,652	3,671	7,508	6,805
Net income	7,207	8,296	15,683	15,587
Assets	3,855,177	3,612,016	3,855,177	3,612,016	3,711,370
Community Banking
Segment Reporting Information [Line Items]
Interest income	35,558	35,025	70,173	69,814
Interest expense	5,753	6,875	11,667	13,657
Provision for loan and lease losses	1,585	1,151	2,249	2,666
Noninterest income	9,306	8,520	17,800	16,078
Noninterest expenses	27,365	24,086	52,232	48,433
Income before income taxes	10,161	11,433	21,825	21,136
Income tax expense	3,379	3,463	6,973	6,314
Net income	6,782	7,970	14,852	14,822
Assets	3,870,262	3,642,323	3,870,262	3,642,323
Insurance Segment
Segment Reporting Information [Line Items]
Interest income	2	2	3	3
Noninterest income	1,026	1,099	2,312	2,390
Noninterest expenses	954	1,141	2,168	2,292
Income before income taxes	74	(40)	147	101
Income tax expense	30	(16)	60	41
Net income	44	(24)	87	60
Assets	13,180	12,708	13,180	12,708
Investment Management Segment
Segment Reporting Information [Line Items]
Interest income	2	2	5	4
Noninterest income	1,364	1,385	2,761	2,731
Noninterest expenses	742	813	1,547	1,580
Income before income taxes	624	574	1,219	1,155
Income tax expense	243	224	475	450
Net income	381	350	744	705
Assets	15,537	14,092	15,537	14,092
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(4)	(21)	(8)	(63)
Interest expense	(4)	(21)	(8)	(63)
Noninterest income	(203)	(202)	(406)	(405)
Noninterest expenses	(203)	(202)	(406)	(405)
Assets	$ (43,802)	$ (57,107)	$ (43,802)	$ (57,107)