Quarterly Financial Results (Unaudited) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended			3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 First Quarter	Mar. 31, 2012 First Quarter	Jun. 30, 2013 Second Quarter	Jun. 30, 2012 Second Quarter	Sep. 30, 2013 Third Quarter	Sep. 30, 2012 Third Quarter	Dec. 31, 2013 Fourth Quarter	Dec. 31, 2012 Fourth Quarter
Effect of Fourth Quarter Events [Line Items]
Interest income	$ 149,347	$ 143,870	$ 139,470	$ 36,279	$ 34,615	$ 35,779	$ 35,558	$ 40,180	$ 37,495	$ 37,109	$ 36,202
Interest expense	19,433	22,651	26,524	4,953	5,910	4,847	5,749	4,874	5,710	4,759	5,282
Net interest income	129,914	121,219	112,946	31,326	28,705	30,932	29,809	35,306	31,785	32,350	30,920
Provision (credit) for loan and lease losses	(1,084)	3,649	1,428	78	664	(2,876)	1,585	1,128	232	586	1,168
Noninterest income	47,511	46,956	43,500	12,419	10,974	12,215	11,493	11,223	12,242	11,654	12,247
Noninterest expense	111,524	109,927	105,071	27,823	26,683	27,508	28,858	26,893	27,167	29,300	27,219
Income before income taxes	66,985	54,599	49,947	15,844	12,332	18,515	10,859	18,508	16,628	14,118	14,780
Income tax expense	22,563	18,045	15,845	5,286	3,856	6,353	3,652	6,419	5,638	4,505	4,899
Net income	$ 44,422	$ 36,554	$ 34,102	$ 10,558	$ 8,476	$ 12,162	$ 7,207	$ 12,089	$ 10,990	$ 9,613	$ 9,881
Basic net income per share	$ 1.78	$ 1.49	$ 1.42	$ 0.42	$ 0.35	$ 0.49	$ 0.30	$ 0.48	$ 0.44	$ 0.38	$ 0.40
Diluted net income per share	$ 1.77	$ 1.48	$ 1.41	$ 0.42	$ 0.35	$ 0.49	$ 0.30	$ 0.48	$ 0.44	$ 0.38	$ 0.40