Segment Reporting - Operating Results and Total Assets Reportable Segments (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) Segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment									4
Net interest income (loss)	$ 185,259	$ 180,197	$ 176,905	$ 176,152	$ 173,340	$ 168,010	$ 163,511	$ 159,764	$ 718,513	$ 664,625	$ 628,441
Provision for loan and lease losses	12,500	14,250	14,000	15,600	13,800	13,000	12,750	9,750	56,350	49,300	37,250
Net interest income (loss) after provision for loan and lease losses									662,163	615,325	591,191
Non-interest income									264,478	237,777	202,108
Non-interest expense	161,871	156,097	152,778	152,445	143,780	139,937	137,537	134,087	623,191	555,341	501,600
Income before income tax expense	81,505	76,262	75,202	70,481	75,439	76,365	72,469	73,488	303,450	297,761	291,699
Income tax expense (benefit)	23,845	24,445	24,599	23,434	23,627	24,995	20,426	23,984	96,323	93,032	91,973
Net income	57,660	$ 51,817	$ 50,603	$ 47,047	51,812	$ 51,370	$ 52,043	$ 49,504	207,127	204,729	199,726
Total Assets	26,072,529				24,641,118				26,072,529	24,641,118
HSA Bank [Member]
Segment Reporting Information [Line Items]
Net income										37,443
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									276,246	255,845	238,186
Provision for loan and lease losses									36,594	30,160	13,088
Net interest income (loss) after provision for loan and lease losses									239,652	225,685	225,098
Non-interest income									47,435	37,784	37,270
Non-interest expense									118,159	109,718	102,374
Income before income tax expense									168,928	153,751	159,994
Income tax expense (benefit)									53,622	48,037	50,446
Net income									115,306	105,714	109,548
Total Assets	8,518,830				7,505,513				8,518,830	7,505,513
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									365,151	354,709	354,781
Provision for loan and lease losses									21,690	19,603	26,345
Net interest income (loss) after provision for loan and lease losses									343,461	335,106	328,436
Non-interest income									110,157	108,604	103,543
Non-interest expense									364,549	330,692	324,312
Income before income tax expense									89,069	113,018	107,667
Income tax expense (benefit)									28,273	35,310	33,947
Net income									60,796	77,708	73,720
Total Assets	8,655,789				8,441,950				8,655,789	8,441,950
Operating Segments [Member] | HSA Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									81,451	73,433	38,822
Provision for loan and lease losses									0	0	0
Net interest income (loss) after provision for loan and lease losses									81,451	73,433	38,822
Non-interest income									71,710	62,475	28,553
Non-interest expense									97,152	81,449	40,900
Income before income tax expense									56,009	54,459	26,475
Income tax expense (benefit)									17,779	17,016	8,311
Net income									38,230	37,443	18,164
Total Assets	83,987				95,815				83,987	95,815
Operating Segments [Member] | Private Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									11,350	10,240	8,877
Provision for loan and lease losses									861	386	765
Net interest income (loss) after provision for loan and lease losses									10,489	9,854	8,112
Non-interest income									9,818	9,183	9,843
Non-interest expense									20,220	19,781	18,691
Income before income tax expense									87	(744)	(736)
Income tax expense (benefit)									27	(233)	(232)
Net income									60	(511)	(504)
Total Assets	550,615				493,571				550,615	493,571
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									(15,685)	(29,602)	(12,225)
Provision for loan and lease losses									(2,795)	(849)	(2,948)
Net interest income (loss) after provision for loan and lease losses									(12,890)	(28,753)	(9,277)
Non-interest income									25,358	19,731	22,899
Non-interest expense									23,111	13,701	15,323
Income before income tax expense									(10,643)	(22,723)	(1,701)
Income tax expense (benefit)									(3,378)	(7,098)	(499)
Net income									(7,265)	(15,625)	$ (1,202)
Total Assets	$ 8,263,308				$ 8,104,269				$ 8,263,308	$ 8,104,269