Investment Securities (Details - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	$ 3,315,534	$ 3,213,655
Available-for-sale Securities, Gross Unrealized Gain	40,453	32,386
Available-for-sale Securities, Gross Unrealized Loss	(18,995)	(22,211)
Securities available‑for‑sale	3,336,992	3,223,830
Government agency and government-sponsored enterprise pass through securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	471,851	499,185
Available-for-sale Securities, Gross Unrealized Gain	6,088	6,222
Available-for-sale Securities, Gross Unrealized Loss	(3,383)	(2,964)
Securities available‑for‑sale	474,556	502,443
Government agency and government-sponsored enterprise collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	137,720	145,258
Available-for-sale Securities, Gross Unrealized Gain	1,661	1,528
Available-for-sale Securities, Gross Unrealized Loss	(449)	(497)
Securities available‑for‑sale	138,932	146,289
Private label collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	147,818	122,707
Available-for-sale Securities, Gross Unrealized Gain	3,461	4,199
Available-for-sale Securities, Gross Unrealized Loss	(1,879)	(1,437)
Securities available‑for‑sale	149,400	125,469
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	1,464,306	1,447,064
Available-for-sale Securities, Gross Unrealized Gain	22,686	15,406
Available-for-sale Securities, Gross Unrealized Loss	(3,711)	(6,011)
Securities available‑for‑sale	1,483,281	1,456,459
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	718,483	555,552
Available-for-sale Securities, Gross Unrealized Gain	2,488	1,798
Available-for-sale Securities, Gross Unrealized Loss	(8,900)	(9,658)
Securities available‑for‑sale	712,071	547,692
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	17,000	47,100
Available-for-sale Securities, Gross Unrealized Gain	1,211	680
Available-for-sale Securities, Gross Unrealized Loss	0	(271)
Securities available‑for‑sale	18,211	47,509
Collateralized loan obligations
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	126,306	155,440
Available-for-sale Securities, Gross Unrealized Gain	1,809	1,685
Available-for-sale Securities, Gross Unrealized Loss	(142)	(238)
Securities available‑for‑sale	127,973	156,887
SBA asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	168,084	179,085
Available-for-sale Securities, Gross Unrealized Gain	589	510
Available-for-sale Securities, Gross Unrealized Loss	(339)	(750)
Securities available‑for‑sale	168,334	178,845
Asset-backed and other securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	63,966	62,264
Available-for-sale Securities, Gross Unrealized Gain	460	358
Available-for-sale Securities, Gross Unrealized Loss	(192)	(385)
Securities available‑for‑sale	$ 64,234	$ 62,237