Segment Results (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income		$ 279,412	$ 289,029	$ 857,277	$ 856,671
Recovery of loan losses		(9,028)	(3,945)	(8,687)	(18,387)
Non-Interest Income		37,587	41,286	151,722	131,114
Non-interest expense	[1]	147,308	145,195	456,074	439,356
Income before income taxes		178,719	189,065	561,612	566,816
Income tax expense		64,031	68,807	203,961	212,616
Net income		114,688	120,258	357,651	354,200
Identifiable segment assets (period-end)		49,045,482	48,679,772	49,045,482	48,679,772	$ 48,559,217
Third Party
Segment Reporting Information [Line Items]
Non-Interest Income	[2]	37,587	41,286	151,722	131,114
Banking Operations
Segment Reporting Information [Line Items]
Net interest income		275,990	285,185	845,281	846,440
Recovery of loan losses		(9,028)	(3,945)	(8,687)	(18,387)
Non-Interest Income		26,074	20,956	96,352	71,868
Non-interest expense	[1]	130,832	130,344	406,459	395,098
Income before income taxes		180,260	179,742	543,861	541,597
Income tax expense		64,654	65,329	196,790	203,217
Net income		115,606	114,413	347,071	338,380
Identifiable segment assets (period-end)		48,342,734	48,016,992	48,342,734	48,016,992
Banking Operations | Third Party
Segment Reporting Information [Line Items]
Non-Interest Income	[2]	29,587	23,989	108,096	82,451
Banking Operations | Inter-segment
Segment Reporting Information [Line Items]
Non-Interest Income		(3,513)	(3,033)	(11,744)	(10,583)
Residential Mortgage Banking
Segment Reporting Information [Line Items]
Net interest income		3,422	3,844	11,996	10,231
Non-Interest Income		11,513	20,330	55,370	59,246
Non-interest expense	[1]	16,476	14,851	49,615	44,258
Income before income taxes		(1,541)	9,323	17,751	25,219
Income tax expense		(623)	3,478	7,171	9,399
Net income		(918)	5,845	10,580	15,820
Identifiable segment assets (period-end)		702,748	662,780	702,748	662,780
Residential Mortgage Banking | Third Party
Segment Reporting Information [Line Items]
Non-Interest Income	[2]	8,000	17,297	43,626	48,663
Residential Mortgage Banking | Inter-segment
Segment Reporting Information [Line Items]
Non-Interest Income		$ 3,513	$ 3,033	$ 11,744	$ 10,583

[1] Includes both direct and indirect expenses.

[2] Includes ancillary fee income.