Segment Results (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income		$ 276,343	$ 318,423	$ 859,029	$ 971,862
Provision (Recovery) of loan losses		44,585	(55)	34,316	664
Gain on sale of mortgage banking operations		7,359		7,359
Non-interest income		108,928	40,595	191,537	113,198
Non-interest expense	[1]	162,234	161,685	492,942	481,044
Income before income taxes		178,452	197,388	523,308	603,352
Income tax expense (benefit)		67,984	72,089	193,628	221,684
Net income (loss)		110,468	125,299	329,680	381,668
Identifiable segment assets (period-end)		48,457,891	49,462,620	48,457,891	49,462,620	$ 48,926,555
Operating Segments
Segment Reporting Information [Line Items]
Non-interest income	[2]	101,569	40,595	184,178	113,198
Banking Operations
Segment Reporting Information [Line Items]
Net interest income		273,265	314,081	850,486	960,661
Provision (Recovery) of loan losses		44,585	(55)	34,316	664
Non-interest income		97,185	22,268	152,999	74,324
Non-interest expense	[1]	146,869	144,504	445,910	430,706
Income before income taxes		178,996	191,900	523,259	603,615
Income tax expense (benefit)		68,200	69,905	193,608	221,817
Net income (loss)		110,796	121,995	329,651	381,798
Identifiable segment assets (period-end)		48,457,891	48,478,288	48,457,891	48,478,288
Banking Operations | Operating Segments
Segment Reporting Information [Line Items]
Non-interest income	[2]	99,596	27,131	163,221	87,616
Banking Operations | Inter-segment
Segment Reporting Information [Line Items]
Non-interest income		(2,411)	(4,863)	(10,222)	(13,292)
Residential Mortgage Banking
Segment Reporting Information [Line Items]
Net interest income		3,078	4,342	8,543	11,201
Gain on sale of mortgage banking operations		7,359		7,359
Non-interest income		11,743	18,327	38,538	38,874
Non-interest expense	[1]	15,365	17,181	47,032	50,338
Income before income taxes		(544)	5,488	49	(263)
Income tax expense (benefit)		(216)	2,184	20	(133)
Net income (loss)		(328)	3,304	29	(130)
Identifiable segment assets (period-end)			984,332		984,332
Residential Mortgage Banking | Operating Segments
Segment Reporting Information [Line Items]
Non-interest income	[2]	1,973	13,464	20,957	25,582
Residential Mortgage Banking | Inter-segment
Segment Reporting Information [Line Items]
Non-interest income		$ 2,411	$ 4,863	$ 10,222	$ 13,292

[1] Includes both direct and indirect expenses.

[2] Includes ancillary fee income.