Quarterly Financial Results (Unaudited) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Interest income	$ 143,870	$ 139,470	$ 148,349
Interest expense	22,651	26,524	32,742
Net interest income	121,219	112,946	115,607
Provision for (credit) loan and lease losses	3,649	1,428	25,908
Noninterest income	46,956	43,500	43,782
Noninterest expenses	109,927	105,071	100,912
Income before income taxes	54,599	49,947	32,569
Income tax expense	18,045	15,845	9,049
Net income	36,554	34,102	23,520
Basic net income per share	$ 1.49	$ 1.42	$ 1.05
Diluted net income per share	$ 1.48	$ 1.41	$ 1.05
First Quarter
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Interest income	34,615	34,750
Interest expense	5,910	6,740
Net interest income	28,705	28,010
Provision for (credit) loan and lease losses	664	1,515
Noninterest income	10,974	9,992
Noninterest expenses	26,683	26,062
Income before income taxes	12,332	10,425
Income tax expense	3,856	3,134
Net income	8,476	7,291
Basic net income per share	$ 0.35	$ 0.30
Diluted net income per share	$ 0.35	$ 0.30
Second Quarter
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Interest income	35,558	35,008
Interest expense	5,749	6,854
Net interest income	29,809	28,154
Provision for (credit) loan and lease losses	1,585	1,151
Noninterest income	11,493	10,802
Noninterest expenses	28,858	25,838
Income before income taxes	10,859	11,967
Income tax expense	3,652	3,671
Net income	7,207	8,296
Basic net income per share	$ 0.30	$ 0.34
Diluted net income per share	$ 0.30	$ 0.34
Third Quarter
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Interest income	37,495	35,004
Interest expense	5,710	6,674
Net interest income	31,785	28,330
Provision for (credit) loan and lease losses	232	(3,520)
Noninterest income	12,242	11,336
Noninterest expenses	27,167	25,848
Income before income taxes	16,628	17,338
Income tax expense	5,638	6,081
Net income	10,990	11,257
Basic net income per share	$ 0.44	$ 0.47
Diluted net income per share	$ 0.44	$ 0.47
Fourth Quarter
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Interest income	36,202	34,708
Interest expense	5,282	6,256
Net interest income	30,920	28,452
Provision for (credit) loan and lease losses	1,168	2,282
Noninterest income	12,247	11,370
Noninterest expenses	27,219	27,323
Income before income taxes	14,780	10,217
Income tax expense	4,899	2,959
Net income	$ 9,881	$ 7,258
Basic net income per share	$ 0.40	$ 0.30
Diluted net income per share	$ 0.40	$ 0.30