Business Segments (Details 2) - 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
Interest income	$ 339,910	$ 280,317	$ 965,354	$ 835,354
Charge for funds used	(132,639)	(81,440)	(378,459)	(252,969)
Interest spread on funds used	207,271	198,877	586,895	582,385
Interest expense	(36,755)	(26,169)	(99,986)	(75,418)
Credit on funds provided	132,639	81,440	378,459	252,969
Interest spread on funds provided (used)	95,884	55,271	278,473	177,551
Net interest income before provision for credit losses	303,155	254,148	865,368	759,936
Provision for credit losses	12,996	9,525	30,749	17,018
Depreciation, amortization and (accretion), net	37,953	35,448	103,771	60,680
Segment income before income taxes	175,284	123,464	560,973	411,051
Goodwill	469,433	469,433	469,433	469,433	$ 469,433
Segment assets	36,307,966	33,255,275	36,307,966	33,255,275	$ 34,788,840
Retail Banking
Segment Reporting Information
Interest income	93,714	77,186	263,491	233,192
Charge for funds used	(37,979)	(24,320)	(98,856)	(70,770)
Interest spread on funds used	55,735	52,866	164,635	162,422
Interest expense	(20,090)	(14,855)	(54,650)	(44,133)
Credit on funds provided	111,812	68,622	320,452	210,831
Interest spread on funds provided (used)	91,722	53,767	265,802	166,698
Net interest income before provision for credit losses	147,457	106,633	430,437	329,120
Provision for credit losses	2,058	(3,709)	1,772	(2,846)
Depreciation, amortization and (accretion), net	3,401	782	6,741	279
Segment income before income taxes	68,554	32,304	204,601	114,513
Goodwill	357,207	357,207	357,207	357,207
Segment assets	8,877,186	7,606,611	8,877,186	7,606,611
Commercial Banking
Segment Reporting Information
Interest income	218,397	180,095	616,689	534,603
Charge for funds used	(87,071)	(53,262)	(229,330)	(159,734)
Interest spread on funds used	131,326	126,833	387,359	374,869
Interest expense	(5,943)	(3,699)	(16,225)	(11,965)
Credit on funds provided	12,770	8,206	37,436	26,655
Interest spread on funds provided (used)	6,827	4,507	21,211	14,690
Net interest income before provision for credit losses	138,153	131,340	408,570	389,559
Provision for credit losses	10,938	13,234	28,977	19,864
Depreciation, amortization and (accretion), net	(5,449)	(5,875)	(14,609)	(25,915)
Segment income before income taxes	99,025	80,393	284,195	268,401
Goodwill	112,226	112,226	112,226	112,226
Segment assets	21,216,848	18,549,562	21,216,848	18,549,562
Other
Segment Reporting Information
Interest income	27,799	23,036	85,174	67,559
Charge for funds used	(7,589)	(3,858)	(50,273)	(22,465)
Interest spread on funds used	20,210	19,178	34,901	45,094
Interest expense	(10,722)	(7,615)	(29,111)	(19,320)
Credit on funds provided	8,057	4,612	20,571	15,483
Interest spread on funds provided (used)	(2,665)	(3,003)	(8,540)	(3,837)
Net interest income before provision for credit losses	17,545	16,175	26,361	41,257
Provision for credit losses	0	0	0	0
Depreciation, amortization and (accretion), net	40,001	40,541	111,639	86,316
Segment income before income taxes	7,705	10,767	72,177	28,137
Goodwill	0	0	0	0
Segment assets	$ 6,213,932	$ 7,099,102	$ 6,213,932	$ 7,099,102