Segment Reporting (Operating Results and Total Assets Reportable Segments) (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]
Total Assets	$ 26,350,182		$ 26,350,182		$ 26,072,529
Net interest income (expense)	200,904	$ 180,197	591,355	$ 533,254
Provision for Loan and Lease Losses	10,150	14,250	27,900	43,850
Net interest income after provision for loan and lease losses	190,754	165,947	563,455	489,404
Noninterest Income	65,846	66,412	193,439	193,861
Total non-interest expense	161,823	156,097	490,026	461,320
Income (loss) before income tax expense	94,777	76,262	266,868	221,945
Income tax expense	30,281	24,445	81,322	72,478
Net income	64,496	51,817	185,546	149,467
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total Assets	9,428,676		9,428,676		9,069,445
Net interest income (expense)	81,925	74,265	239,118	211,422
Provision for Loan and Lease Losses	12,073	7,876	29,562	29,765
Net interest income after provision for loan and lease losses	69,852	66,389	209,556	181,657
Noninterest Income	13,207	15,916	39,163	41,819
Total non-interest expense	38,339	35,793	113,767	103,336
Income (loss) before income tax expense	44,720	46,512	134,952	120,140
Income tax expense	14,363	14,957	41,125	39,233
Net income	30,357	31,555	93,827	80,907
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Total Assets	8,881,322		8,881,322		8,721,046
Net interest income (expense)	96,859	91,995	286,351	274,186
Provision for Loan and Lease Losses	(1,923)	6,374	(1,662)	14,085
Net interest income after provision for loan and lease losses	98,782	85,621	288,013	260,101
Noninterest Income	27,079	29,130	80,516	83,248
Total non-interest expense	92,478	92,508	281,979	276,045
Income (loss) before income tax expense	33,383	22,243	86,550	67,304
Income tax expense	10,605	7,122	26,374	21,979
Net income	22,778	15,121	60,176	45,325
Operating Segments [Member] | HSA Bank [Member]
Segment Reporting Information [Line Items]
Total Assets	76,090		76,090		83,987
Net interest income (expense)	26,713	20,560	76,339	60,484
Provision for Loan and Lease Losses	0	0	0	0
Net interest income after provision for loan and lease losses	26,713	20,560	76,339	60,484
Noninterest Income	19,371	16,900	58,392	54,969
Total non-interest expense	27,222	23,021	84,211	71,966
Income (loss) before income tax expense	18,862	14,439	50,520	43,487
Income tax expense	6,006	4,624	15,395	14,201
Net income	12,856	9,815	35,125	29,286
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Total Assets	7,964,094		7,964,094		$ 8,198,051
Net interest income (expense)	(4,593)	(6,623)	(10,453)	(12,838)
Provision for Loan and Lease Losses	0	0	0	0
Net interest income after provision for loan and lease losses	(4,593)	(6,623)	(10,453)	(12,838)
Noninterest Income	6,189	4,466	15,368	13,825
Total non-interest expense	3,784	4,775	10,069	9,973
Income (loss) before income tax expense	(2,188)	(6,932)	(5,154)	(8,986)
Income tax expense	(693)	(2,258)	(1,572)	(2,935)
Net income	$ (1,495)	$ (4,674)	$ (3,582)	$ (6,051)