Investment Securities (Details 1) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	$ 3,158,551	$ 3,512,385
Available-for-sale Securities, Gross Unrealized Gain	92,003	62,157
Available-for-sale Securities, Gross Unrealized Loss	(9,968)	(15,105)
Securities available‑for‑sale	3,240,586	3,559,437
Government agency and government-sponsored enterprise pass through securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	642,233	759,881
Available-for-sale Securities, Gross Unrealized Gain	12,865	12,075
Available-for-sale Securities, Gross Unrealized Loss	(1,233)	(4,159)
Securities available‑for‑sale	653,865	767,797
Government agency and government-sponsored enterprise collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	431,456	486,065
Available-for-sale Securities, Gross Unrealized Gain	12,515	3,584
Available-for-sale Securities, Gross Unrealized Loss	(239)	(3,410)
Securities available‑for‑sale	443,732	486,239
Covered private label collateralized mortgage obligation
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	23,026	24,113
Available-for-sale Securities, Gross Unrealized Gain	5,064	5,794
Available-for-sale Securities, Gross Unrealized Loss	(227)	(125)
Securities available‑for‑sale	27,863	29,782
Other Private Label Collateralized Mortgage Obligations
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	108,019	115,952
Available-for-sale Securities, Gross Unrealized Gain	246	43
Available-for-sale Securities, Gross Unrealized Loss	(883)	(981)
Securities available‑for‑sale	107,382	115,014
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	1,457,795	1,508,968
Available-for-sale Securities, Gross Unrealized Gain	59,886	39,435
Available-for-sale Securities, Gross Unrealized Loss	(89)	(1,072)
Securities available‑for‑sale	1,517,592	1,547,331
US Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	0	70,196
Available-for-sale Securities, Gross Unrealized Gain	0	0
Available-for-sale Securities, Gross Unrealized Loss	0	(816)
Securities available‑for‑sale	0	69,380
Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	47,269	49,047
Available-for-sale Securities, Gross Unrealized Gain	303	327
Available-for-sale Securities, Gross Unrealized Loss	(2,089)	(950)
Securities available‑for‑sale	45,483	48,424
Collateralized Loan Obligations
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	142,637	133,192
Available-for-sale Securities, Gross Unrealized Gain	42	128
Available-for-sale Securities, Gross Unrealized Loss	(3,107)	(1,131)
Securities available‑for‑sale	139,572	132,189
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	201,934	211,946
Available-for-sale Securities, Gross Unrealized Gain	947	41
Available-for-sale Securities, Gross Unrealized Loss	(207)	(830)
Securities available‑for‑sale	202,674	211,157
US Government-sponsored Enterprises Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	0	36,302
Available-for-sale Securities, Gross Unrealized Gain	0	611
Available-for-sale Securities, Gross Unrealized Loss	0	0
Securities available‑for‑sale	0	36,913
Asset-backed and other securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	104,182	116,723
Available-for-sale Securities, Gross Unrealized Gain	135	119
Available-for-sale Securities, Gross Unrealized Loss	(1,894)	(1,631)
Securities available‑for‑sale	$ 102,423	$ 115,211