Segment Reporting - Operating Results and Total Assets Reportable Segments (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Segment									4
Net interest income (loss)	$ 173,340	$ 168,010	$ 163,511	$ 159,764	$ 160,648	$ 157,370	$ 155,122	$ 155,301	$ 664,625	$ 628,441	$ 596,728
Provision for loan and lease losses	13,800	13,000	12,750	9,750	9,500	9,500	9,250	9,000	49,300	37,250	33,500
Net interest income (loss) after provision for loan and lease losses									615,325	591,191	563,228
Non-interest income									239,545	202,108	191,050
Non-interest expense	143,164	139,854	137,446	134,090	130,164	124,498	122,475	124,463	554,554	501,600	497,709
Income before income tax expense	76,725	76,611	73,166	73,814	74,759	74,281	70,993	71,666	300,316	291,699	256,569
Income tax expense (benefit)	24,146	25,075	20,663	24,092	23,753	23,824	23,159	21,237	93,976	91,973	77,113
Net income	52,579	$ 51,536	$ 52,503	$ 49,722	51,006	$ 50,457	$ 47,834	$ 50,429	206,340	199,726	179,456
Total Assets	24,677,820				22,533,172				24,677,820	22,533,172	20,853,145
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									255,845	238,186	217,582
Provision for loan and lease losses									30,160	13,088	17,971
Net interest income (loss) after provision for loan and lease losses									225,685	225,098	199,611
Non-interest income									37,784	37,270	30,797
Non-interest expense									109,718	102,374	99,801
Income before income tax expense									153,751	159,994	130,607
Income tax expense (benefit)									48,112	50,446	39,260
Net income									105,639	109,548	91,347
Total Assets	7,505,513				6,550,868				7,505,513	6,550,868	5,682,129
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									354,709	354,781	347,395
Provision for loan and lease losses									19,603	26,345	19,219
Net interest income (loss) after provision for loan and lease losses									335,106	328,436	328,176
Non-interest income									108,604	103,543	116,182
Non-interest expense									330,692	324,312	337,795
Income before income tax expense									113,018	107,667	106,563
Income tax expense (benefit)									35,366	33,947	32,029
Net income									77,652	73,720	74,534
Total Assets	8,441,950				8,123,928				8,441,950	8,123,928	7,738,597
Operating Segments [Member] | HSA Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									73,433	38,822	32,807
Provision for loan and lease losses									0	0	0
Net interest income (loss) after provision for loan and lease losses									73,433	38,822	32,807
Non-interest income									64,243	28,553	21,963
Non-interest expense									80,662	40,900	29,962
Income before income tax expense									57,014	26,475	24,808
Income tax expense (benefit)									17,841	8,311	7,423
Net income									39,173	18,164	17,385
Total Assets	95,815				26,680				95,815	26,680	19,524
Operating Segments [Member] | Private Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									10,240	8,877	8,185
Provision for loan and lease losses									386	765	397
Net interest income (loss) after provision for loan and lease losses									9,854	8,112	7,788
Non-interest income									9,183	9,843	10,963
Non-interest expense									19,781	18,691	19,783
Income before income tax expense									(744)	(736)	(1,032)
Income tax expense (benefit)									(233)	(232)	(310)
Net income									(511)	(504)	(722)
Total Assets	493,571				398,893				493,571	398,893	346,338
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)									(29,602)	(12,225)	(9,241)
Provision for loan and lease losses									(849)	(2,948)	(4,087)
Net interest income (loss) after provision for loan and lease losses									(28,753)	(9,277)	(5,154)
Non-interest income									19,731	22,899	11,145
Non-interest expense									13,701	15,323	10,368
Income before income tax expense									(22,723)	(1,701)	(4,377)
Income tax expense (benefit)									(7,110)	(499)	(1,289)
Net income									(15,613)	(1,202)	(3,088)
Total Assets	$ 8,140,971				$ 7,432,803				$ 8,140,971	$ 7,432,803	$ 7,066,557