Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financial information by business segment
Interest income	$ 54,892	$ 53,680
Interest expense	8,764	11,850
Net interest income	46,128	41,830
Provision for credit losses	2,102	6,202
Net interest income after provision for credit losses	44,026	35,628
Non-interest income	17,496	15,322
Non-interest expense	40,747	35,665
Income before provision for income taxes	20,775	15,285
Provision for income taxes	4,754	3,295
Net income	16,021	11,990
Community Banking [Member]
Financial information by business segment
Interest income	54,892	53,680
Interest expense	8,764	11,850
Net interest income	46,128	41,830
Provision for credit losses	2,102	6,202
Net interest income after provision for credit losses	44,026	35,628
Non-interest income	12,478	10,569
Non-interest expense	37,752	32,808
Income before provision for income taxes	18,752	13,389
Provision for income taxes	3,945	2,536
Net income	14,807	10,853
Trust and Investment Services [Member]
Financial information by business segment
Interest income
Interest expense
Net interest income
Provision for credit losses
Net interest income after provision for credit losses
Non-interest income	5,018	4,753
Non-interest expense	2,995	2,857
Income before provision for income taxes	2,023	1,896
Provision for income taxes	809	759
Net income	$ 1,214	$ 1,137