Business Segments (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information
Interest income	$ 322,775	$ 278,865	$ 625,444	$ 555,037
Charge for funds used	(125,405)	(83,249)	(245,820)	(171,529)
Interest spread on funds used	197,370	195,616	379,624	383,508
Interest expense	(32,684)	(25,281)	(63,231)	(49,249)
Credit on funds provided	125,405	83,249	245,820	171,529
Interest spread on funds provided (used)	92,721	57,968	182,589	122,280
Net interest income before provision for credit losses	290,091	253,584	562,213	505,788
(Reversal of) provision for credit losses	10,685	6,053	17,753	7,493
Depreciation, amortization and (accretion), net	37,688	12,474	65,818	25,232
Segment income before income taxes	157,685	142,916	385,689	287,587
Goodwill	469,433	469,433	469,433	469,433	$ 469,433
Segment assets	35,917,617	32,952,212	35,917,617	32,952,212	$ 34,788,840
Retail Banking
Segment Reporting Information
Interest income	88,753	78,635	169,777	156,006
Charge for funds used	(33,139)	(23,798)	(60,877)	(46,450)
Interest spread on funds used	55,614	54,837	108,900	109,556
Interest expense	(18,378)	(14,672)	(34,560)	(29,278)
Credit on funds provided	106,094	69,778	208,640	142,209
Interest spread on funds provided (used)	87,716	55,106	174,080	112,931
Net interest income before provision for credit losses	143,330	109,943	282,980	222,487
(Reversal of) provision for credit losses	(664)	2,445	(286)	863
Depreciation, amortization and (accretion), net	996	(546)	3,340	(503)
Segment income before income taxes	63,360	36,264	136,047	82,209
Goodwill	357,207	357,207	357,207	357,207
Segment assets	8,438,706	7,437,534	8,438,706	7,437,534
Commercial Banking
Segment Reporting Information
Interest income	205,873	177,426	398,292	354,508
Charge for funds used	(77,750)	(52,681)	(142,259)	(106,472)
Interest spread on funds used	128,123	124,745	256,033	248,036
Interest expense	(5,183)	(4,240)	(10,282)	(8,266)
Credit on funds provided	12,624	8,472	24,666	18,449
Interest spread on funds provided (used)	7,441	4,232	14,384	10,183
Net interest income before provision for credit losses	135,564	128,977	270,417	258,219
(Reversal of) provision for credit losses	11,349	3,608	18,039	6,630
Depreciation, amortization and (accretion), net	(5,686)	(9,267)	(9,160)	(20,040)
Segment income before income taxes	92,699	95,179	185,170	188,008
Goodwill	112,226	112,226	112,226	112,226
Segment assets	20,456,579	18,196,664	20,456,579	18,196,664
Other
Segment Reporting Information
Interest income	28,149	22,804	57,375	44,523
Charge for funds used	(14,516)	(6,770)	(42,684)	(18,607)
Interest spread on funds used	13,633	16,034	14,691	25,916
Interest expense	(9,123)	(6,369)	(18,389)	(11,705)
Credit on funds provided	6,687	4,999	12,514	10,871
Interest spread on funds provided (used)	(2,436)	(1,370)	(5,875)	(834)
Net interest income before provision for credit losses	11,197	14,664	8,816	25,082
(Reversal of) provision for credit losses	0	0	0	0
Depreciation, amortization and (accretion), net	42,378	22,287	71,638	45,775
Segment income before income taxes	1,626	11,473	64,472	17,370
Goodwill	0	0	0	0
Segment assets	$ 7,022,332	$ 7,318,014	$ 7,022,332	$ 7,318,014