Business Segments - Operating Results and Total Assets Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012		Jun. 30, 2013 Segment	Jun. 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	94.30%			104.50%
Net interest income (loss)	$ 147,061	$ 144,378		$ 292,857	$ 287,746
(Benefit) provision for loan and lease losses	8,500	5,000		16,000	9,000
Net interest income after provision for loan and lease losses	138,561	139,378		276,857	278,746
Non-interest income	52,251	47,353		100,529	91,339
Non-interest expense	123,604	127,179		249,139	254,992
Income before income tax expense	67,208	59,552		128,247	115,093
Income tax expense	20,835	18,312		39,757	34,915
Net income	46,373	41,240		88,490	80,178
Total Assets	20,329,238			20,329,238			20,146,765
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	53,418	45,574	[1]	104,578	89,483	[1]
(Benefit) provision for loan and lease losses	2,416	(4,529)	[1]	4,417	(5,439)	[1]
Net interest income after provision for loan and lease losses	51,002	50,103	[1]	100,161	94,922	[1]
Non-interest income	6,887	7,281	[1]	11,719	14,174	[1]
Non-interest expense	24,151	24,804	[1]	49,421	49,497	[1]
Income before income tax expense	33,738	32,580	[1]	62,459	59,599	[1]
Income tax expense	10,460	10,003	[1]	19,363	18,080	[1]
Net income	23,278	22,577	[1]	43,096	41,519	[1]
Total Assets	5,291,138			5,291,138			5,113,898
Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	86,421	85,907	[1]	171,088	169,615	[1]
(Benefit) provision for loan and lease losses	5,533	8,069	[1]	12,246	11,138	[1]
Net interest income after provision for loan and lease losses	80,888	77,838	[1]	158,842	158,477	[1]
Non-interest income	31,706	26,414	[1]	62,267	54,073	[1]
Non-interest expense	83,142	86,034	[1]	169,011	172,884	[1]
Income before income tax expense	29,452	18,218	[1]	52,098	39,666	[1]
Income tax expense	9,130	5,621	[1]	16,150	12,033	[1]
Net income	20,322	12,597	[1]	35,948	27,633	[1]
Total Assets	7,698,944			7,698,944			7,708,159
Other [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	9,987	8,379	[1]	19,275	16,298	[1]
(Benefit) provision for loan and lease losses	69	(262)	[1]	50	(340)	[1]
Net interest income after provision for loan and lease losses	9,918	8,641	[1]	19,225	16,638	[1]
Non-interest income	8,351	7,281	[1]	16,496	14,414	[1]
Non-interest expense	12,388	10,695	[1]	25,199	22,228	[1]
Income before income tax expense	5,881	5,227	[1]	10,522	8,824	[1]
Income tax expense	1,823	1,602	[1]	3,262	2,677	[1]
Net income	4,058	3,625	[1]	7,260	6,147	[1]
Total Assets	317,169			317,169			282,414
Total Business Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	149,826	139,860	[1]	294,941	275,396	[1]
(Benefit) provision for loan and lease losses	8,018	3,278	[1]	16,713	5,359	[1]
Net interest income after provision for loan and lease losses	141,808	136,582	[1]	278,228	270,037	[1]
Non-interest income	46,944	40,976	[1]	90,482	82,661	[1]
Non-interest expense	119,681	121,533	[1]	243,631	244,609	[1]
Income before income tax expense	69,071	56,025	[1]	125,079	108,089	[1]
Income tax expense	21,413	17,226	[1]	38,775	32,790	[1]
Net income	47,658	38,799	[1]	86,304	75,299	[1]
Total Assets	13,307,251			13,307,251			13,104,471
Corporate and Reconciling [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	(2,765)	4,518	[1]	(2,084)	12,350	[1]
(Benefit) provision for loan and lease losses	482	1,722	[1]	(713)	3,641	[1]
Net interest income after provision for loan and lease losses	(3,247)	2,796	[1]	(1,371)	8,709	[1]
Non-interest income	5,307	6,377	[1]	10,047	8,678	[1]
Non-interest expense	3,923	5,646	[1]	5,508	10,383	[1]
Income before income tax expense	(1,863)	3,527	[1]	3,168	7,004	[1]
Income tax expense	(578)	1,086	[1]	982	2,125	[1]
Net income	(1,285)	2,441	[1]	2,186	4,879	[1]
Total Assets	7,021,987			7,021,987			7,042,294
Consolidated Business Segments [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	147,061	144,378	[1]	292,857	287,746	[1]
(Benefit) provision for loan and lease losses	8,500	5,000	[1]	16,000	9,000	[1]
Net interest income after provision for loan and lease losses	138,561	139,378	[1]	276,857	278,746	[1]
Non-interest income	52,251	47,353	[1]	100,529	91,339	[1]
Non-interest expense	123,604	127,179	[1]	249,139	254,992	[1]
Income before income tax expense	67,208	59,552	[1]	128,247	115,093	[1]
Income tax expense	20,835	18,312	[1]	39,757	34,915	[1]
Net income	46,373	41,240	[1]	88,490	80,178	[1]
Total Assets	$ 20,329,238			$ 20,329,238			$ 20,146,765

[1] Reclassified to conform to the 2013 presentation.