Business Segments - Schedule of Financial Data for Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 19,829,312				$ 17,425,504				$ 19,829,312	$ 17,425,504	$ 15,040,783
Interest income	201,095	$ 191,203	$ 189,028	$ 185,597	185,594	$ 174,690	$ 175,754	$ 170,985	766,923	707,023	636,603
Interest expense	36,700	37,057	37,573	37,444	37,548	40,730	39,577	38,899	148,774	156,754	161,846
Net Interest Income	164,395	154,146	151,455	148,153	148,046	133,960	136,177	132,086	618,149	550,269	474,757
Provision for credit losses	3,800	5,840	1,429	800	3,507	94	4,500	0	11,869	8,101	1,884
Net Interest Income After Provision for Credit Losses									606,280	542,168	472,873
Non-interest income									103,225	83,802	77,616
Non-interest expense:									476,125	499,075	403,255
Internal expense transfer									0	0	0
Income before income taxes	$ 68,426	$ 59,891	$ 54,487	$ 50,576	$ (6,316)	$ 46,133	$ 44,465	$ 42,613	$ 233,380	$ 126,895	$ 147,234
Return on average interest earning assets (pre-tax)	1.18%				0.73%				1.18%	0.73%	0.98%
Corporate and Other Adjustments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 0				$ 0				$ 0	$ 0	$ 0
Interest income									(8,760)	(8,277)	(8,356)
Interest expense									11,520	11,233	11,007
Net Interest Income									(20,280)	(19,510)	(19,363)
Provision for credit losses									0	0	0
Net Interest Income After Provision for Credit Losses									(20,280)	(19,510)	(19,363)
Non-interest income									29,796	30,937	50,237
Non-interest expense:									341,978	370,051	284,693
Internal expense transfer									(280,251)	(264,364)	(239,002)
Income before income taxes									(52,211)	(94,260)	(14,817)
Consumer Lending | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 5,081,798				$ 4,764,306				5,081,798	4,764,306	4,122,468
Interest income									176,929	170,569	154,078
Interest expense									35,175	39,787	41,343
Net Interest Income									141,754	130,782	112,735
Provision for credit losses									905	1,153	438
Net Interest Income After Provision for Credit Losses									140,849	129,629	112,297
Non-interest income									63,443	45,306	40,611
Non-interest expense:									62,721	59,794	59,051
Internal expense transfer									71,578	72,441	65,477
Income before income taxes									$ 69,993	$ 42,700	$ 28,380
Return on average interest earning assets (pre-tax)	1.38%				0.90%				1.38%	0.90%	0.69%
Commercial Lending | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 11,318,947				$ 9,682,714				$ 11,318,947	$ 9,682,714	$ 7,959,215
Interest income									509,376	463,062	399,192
Interest expense									78,347	80,861	79,820
Net Interest Income									431,029	382,201	319,372
Provision for credit losses									10,964	6,948	1,446
Net Interest Income After Provision for Credit Losses									420,065	375,253	317,926
Non-interest income									3,292	744	(19,624)
Non-interest expense:									70,145	68,156	58,142
Internal expense transfer									160,198	146,463	126,465
Income before income taxes									$ 193,014	$ 161,378	$ 113,695
Return on average interest earning assets (pre-tax)	1.71%				1.67%				1.71%	1.67%	1.43%
Investment Management | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 3,428,567				$ 2,978,484				$ 3,428,567	$ 2,978,484	$ 2,959,100
Interest income									89,378	81,669	91,689
Interest expense									23,732	24,873	29,676
Net Interest Income									65,646	56,796	62,013
Provision for credit losses									0	0	0
Net Interest Income After Provision for Credit Losses									65,646	56,796	62,013
Non-interest income									6,694	6,815	6,392
Non-interest expense:									1,281	1,074	1,369
Internal expense transfer									48,475	45,460	47,060
Income before income taxes									$ 22,584	$ 17,077	$ 19,976
Return on average interest earning assets (pre-tax)	0.66%				0.57%				0.66%	0.57%	0.68%