Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Information about reportable segments and reconciliation
Net interest income	$ 154,355	$ 156,360	$ 151,576
Provision charged to operations	12,200	16,800	24,368
Net interest income after provision for loan losses	142,155	139,560	127,208
Noninterest income	41,068	32,964	34,217
Noninterest expenses	133,479	130,815	129,920
Income before income taxes	49,744	41,709	31,505
Income tax expense	14,333	11,264	8,583
Net income	35,411	30,445	22,922
Total assets	4,095,865	3,907,087
Community Bank [Member]
Information about reportable segments and reconciliation
Net interest income	153,024	155,045	149,353
Provision charged to operations	12,200	16,800	24,368
Net interest income after provision for loan losses	140,824	138,245	124,985
Noninterest income	24,876	22,382	22,882
Noninterest expenses	119,976	121,490	121,381
Income before income taxes	45,724	39,137	26,486
Income tax expense	12,858	10,304	6,692
Net income	32,866	28,833	19,794
Total assets	4,081,544	3,904,013	3,828,954
Mortgage [Member]
Information about reportable segments and reconciliation
Net interest income	1,331	1,315	2,223
Net interest income after provision for loan losses	1,331	1,315	2,223
Noninterest income	16,660	11,050	11,803
Noninterest expenses	13,971	9,793	9,007
Income before income taxes	4,020	2,572	5,019
Income tax expense	1,475	960	1,891
Net income	2,545	1,612	3,128
Total assets	187,836	84,445	82,255
Eliminations [Member]
Information about reportable segments and reconciliation
Noninterest income	(468)	(468)	(468)
Noninterest expenses	(468)	(468)	(468)
Total assets	(173,515)	(81,371)	(73,962)
Consolidated Totals [Member]
Information about reportable segments and reconciliation
Net interest income	154,355	156,360	151,576
Provision charged to operations	12,200	16,800	24,368
Net interest income after provision for loan losses	142,155	139,560	127,208
Noninterest income	41,068	32,964	34,217
Noninterest expenses	133,479	130,815	129,920
Income before income taxes	49,744	41,709	31,505
Income tax expense	14,333	11,264	8,583
Net income	35,411	30,445	22,922
Total assets	$ 4,095,865	$ 3,907,087	$ 3,837,247