Business Segments - Operating Results and Total Assets Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2013 Segment	Sep. 30, 2012		Dec. 31, 2012 Segment
Segment Reporting Information [Line Items]
Number of Reportable Segments				3			4
Percentage of provision expense attributable to business segments	125.00%			111.60%
Net interest income (loss)	$ 149,987	$ 144,890		$ 442,844	$ 432,636
(Benefit) provision for loan and lease losses	8,500	5,000		24,500	14,000
Net interest income after provision for loan and lease losses	141,487	139,890		418,344	418,636
Non-interest income	46,257	48,479		146,786	139,818
Non-interest expense	122,281	123,887		371,420	378,879
Income before income tax expense	65,463	64,482		193,710	179,575
Income tax expense	18,158	19,489		57,915	54,404
Net income	47,305	44,993		135,795	125,171
Total Assets	20,609,554			20,609,554			20,146,765
Consolidated Business Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	149,987	144,890	[1]	442,844	432,636	[1]
(Benefit) provision for loan and lease losses	8,500	5,000	[1]	24,500	14,000	[1]
Net interest income after provision for loan and lease losses	141,487	139,890	[1]	418,344	418,636	[1]
Non-interest income	46,257	48,479	[1]	146,786	139,818	[1]
Non-interest expense	122,281	123,887	[1]	371,420	378,879	[1]
Income before income tax expense	65,463	64,482	[1]	193,710	179,575	[1]
Income tax expense	18,158	19,489	[1]	57,915	54,404	[1]
Net income	47,305	44,993	[1]	135,795	125,171	[1]
Total Assets	20,609,554			20,609,554			20,146,765
Total Business Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	155,112	142,916	[1]	450,053	418,312	[1]
(Benefit) provision for loan and lease losses	10,624	3,841	[1]	27,337	9,200	[1]
Net interest income after provision for loan and lease losses	144,488	139,075	[1]	422,716	409,112	[1]
Non-interest income	42,288	44,642	[1]	132,770	127,303	[1]
Non-interest expense	119,308	120,196	[1]	362,939	364,805	[1]
Income before income tax expense	67,468	63,521	[1]	192,547	171,610	[1]
Income tax expense	18,792	19,201	[1]	57,567	51,991	[1]
Net income	48,676	44,320	[1]	134,980	119,619	[1]
Total Assets	13,547,310			13,547,310			13,104,471
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	56,430	48,127	[1]	161,008	137,610	[1]
(Benefit) provision for loan and lease losses	7,032	(5,540)	[1]	11,449	(10,979)	[1]
Net interest income after provision for loan and lease losses	49,398	53,667	[1]	149,559	148,589	[1]
Non-interest income	8,818	7,191	[1]	20,537	21,365	[1]
Non-interest expense	24,647	24,823	[1]	74,068	74,320	[1]
Income before income tax expense	33,569	36,035	[1]	96,028	95,634	[1]
Income tax expense	9,347	10,893	[1]	28,710	28,973	[1]
Net income	24,222	25,142	[1]	67,318	66,661	[1]
Total Assets	5,517,704			5,517,704			5,113,898
Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	87,949	86,263	[1]	259,037	255,878	[1]
(Benefit) provision for loan and lease losses	3,570	9,709	[1]	15,816	20,847	[1]
Net interest income after provision for loan and lease losses	84,379	76,554	[1]	243,221	235,031	[1]
Non-interest income	25,387	30,312	[1]	87,654	84,385	[1]
Non-interest expense	82,748	84,408	[1]	251,759	257,292	[1]
Income before income tax expense	27,018	22,458	[1]	79,116	62,124	[1]
Income tax expense	7,504	6,788	[1]	23,654	18,821	[1]
Net income	19,514	15,670	[1]	55,462	43,303	[1]
Total Assets	7,703,557			7,703,557			7,708,159
Other [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	10,733	8,526	[1]	30,008	24,824	[1]
(Benefit) provision for loan and lease losses	22	(328)	[1]	72	(668)	[1]
Net interest income after provision for loan and lease losses	10,711	8,854	[1]	29,936	25,492	[1]
Non-interest income	8,083	7,139	[1]	24,579	21,553	[1]
Non-interest expense	11,913	10,965	[1]	37,112	33,193	[1]
Income before income tax expense	6,881	5,028	[1]	17,403	13,852	[1]
Income tax expense	1,941	1,520	[1]	5,203	4,197	[1]
Net income	4,940	3,508	[1]	12,200	9,655	[1]
Total Assets	326,049			326,049			282,414
Corporate and Reconciling [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	(5,125)	1,974	[1]	(7,209)	14,324	[1]
(Benefit) provision for loan and lease losses	(2,124)	1,159	[1]	(2,837)	4,800	[1]
Net interest income after provision for loan and lease losses	(3,001)	815	[1]	(4,372)	9,524	[1]
Non-interest income	3,969	3,837	[1]	14,016	12,515	[1]
Non-interest expense	2,973	3,691	[1]	8,481	14,074	[1]
Income before income tax expense	(2,005)	961	[1]	1,163	7,965	[1]
Income tax expense	(634)	288	[1]	348	2,413	[1]
Net income	(1,371)	673	[1]	815	5,552	[1]
Total Assets	$ 7,062,244			$ 7,062,244			$ 7,042,294

[1] Reclassified to conform to the 2013 presentation.