Business Segments - Financial Information by Business Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Interest income	$ 54,424	$ 52,545	$ 109,317	$ 106,226
Interest expense	8,435	11,005	17,199	22,855
Net interest income	45,989	41,540	92,118	83,371
Provision for credit losses	1,021	5,903	3,123	12,105
Net interest income after provision for credit losses	44,968	35,637	88,995	71,266
Non-interest income	17,724	15,894	35,220	31,215
Non-interest expense	39,499	36,084	80,246	71,749
Income before provision for income taxes	23,193	15,447	43,969	30,732
Provision for income taxes	6,176	3,449	10,932	6,744
Net income	17,017	11,998	33,037	23,988
Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	54,424	52,545	109,317	106,226
Interest expense	8,435	11,005	17,199	22,855
Net interest income	45,989	41,540	92,118	83,371
Provision for credit losses	1,021	5,903	3,123	12,105
Net interest income after provision for credit losses	44,968	35,637	88,995	71,266
Non-interest income	12,901	11,636	25,380	22,204
Non-interest expense	36,620	33,446	74,372	66,254
Income before provision for income taxes	21,249	13,827	40,003	27,216
Provision for income taxes	5,399	2,802	9,346	5,338
Net income	15,850	11,025	30,657	21,878
Trust and Investment Services [Member]
Segment Reporting Information [Line Items]
Non-interest income	4,823	4,258	9,840	9,011
Non-interest expense	2,879	2,638	5,874	5,495
Income before provision for income taxes	1,944	1,620	3,966	3,516
Provision for income taxes	777	647	1,586	1,406
Net income	$ 1,167	$ 973	$ 2,380	$ 2,110