Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Financial Information by Business Segment
Interest income	$ 52,545	$ 57,042	$ 106,226	$ 113,139
Interest expense	11,005	13,989	22,855	28,610
Net interest income	41,540	43,053	83,371	84,529
Provision for credit losses	5,903	6,802	12,105	14,843
Net interest income after provision for credit losses	35,637	36,251	71,266	69,686
Non-interest income	15,894	15,016	31,215	29,521
Non-interest expense	36,084	35,703	71,749	71,194
Income before provision for income taxes	15,447	15,564	30,732	28,013
Provision for income taxes	3,449	3,646	6,744	5,854
Net income	11,998	11,918	23,988	22,159
Community Banking [Member]
Financial Information by Business Segment
Interest income	52,545	57,042	106,226	113,139
Interest expense	11,005	13,989	22,855	28,610
Net interest income	41,540	43,053	83,371	84,529
Provision for credit losses	5,903	6,802	12,105	14,843
Net interest income after provision for credit losses	35,637	36,251	71,266	69,686
Non-interest income	11,636	10,744	22,204	20,487
Non-interest expense	33,446	33,208	66,254	66,122
Income before provision for income taxes	13,827	13,787	27,216	24,051
Provision for income taxes	2,802	2,935	5,338	4,269
Net income	11,025	10,852	21,878	19,782
Trust and Investment Services [Member]
Financial Information by Business Segment
Interest income	0	0	0	0
Interest expense	0	0	0	0
Net interest income	0	0	0	0
Provision for credit losses	0	0	0	0
Net interest income after provision for credit losses	0	0	0	0
Non-interest income	4,258	4,272	9,011	9,034
Non-interest expense	2,638	2,495	5,495	5,072
Income before provision for income taxes	1,620	1,777	3,516	3,962
Provision for income taxes	647	711	1,406	1,585
Net income	$ 973	$ 1,066	$ 2,110	$ 2,377