Investment Securities (Details 1) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	$ 1,768,186	$ 1,522,871
Available-for-sale Securities, Gross Unrealized Gain	47,765	47,908
Available-for-sale Securities, Gross Unrealized Loss	(6,587)	(3,602)
Securities available‑for‑sale	1,809,364	1,567,177
Government agency and government-sponsored enterprise pass through securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	391,904	515,902
Available-for-sale Securities, Gross Unrealized Gain	15,890	20,142
Available-for-sale Securities, Gross Unrealized Loss	(196)	(372)
Securities available‑for‑sale	407,598	535,672
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	206,380	275,513
Available-for-sale Securities, Gross Unrealized Gain	5,460	3,513
Available-for-sale Securities, Gross Unrealized Loss	(421)	(1,080)
Securities available‑for‑sale	211,419	277,946
Covered private label collateralized mortgage obligation [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	24,914	26,889
Available-for-sale Securities, Gross Unrealized Gain	6,222	7,153
Available-for-sale Securities, Gross Unrealized Loss	(110)	(95)
Securities available‑for‑sale	31,026	33,947
Other Private Label Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	7,258	10,961
Available-for-sale Securities, Gross Unrealized Gain	44	46
Available-for-sale Securities, Gross Unrealized Loss	(40)	(93)
Securities available‑for‑sale	7,262	10,914
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	844,782	521,499
Available-for-sale Securities, Gross Unrealized Gain	18,057	15,899
Available-for-sale Securities, Gross Unrealized Loss	(4,002)	(1,282)
Securities available‑for‑sale	858,837	536,116
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	47,380	110,074
Available-for-sale Securities, Gross Unrealized Gain	139	597
Available-for-sale Securities, Gross Unrealized Loss	(123)	(562)
Securities available‑for‑sale	47,396	110,109
Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	133,159	0
Available-for-sale Securities, Gross Unrealized Gain	316	0
Available-for-sale Securities, Gross Unrealized Loss	(1,158)	0
Securities available‑for‑sale	132,317	0
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	36,284	36,232
Available-for-sale Securities, Gross Unrealized Gain	1,240	525
Available-for-sale Securities, Gross Unrealized Loss	0	0
Securities available‑for‑sale	37,524	36,757
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	24,972	25,801
Available-for-sale Securities, Gross Unrealized Gain	2	33
Available-for-sale Securities, Gross Unrealized Loss	(537)	(118)
Securities available‑for‑sale	24,437	25,716
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	51,153	0
Available-for-sale Securities, Gross Unrealized Gain	395	0
Available-for-sale Securities, Gross Unrealized Loss	0	0
Securities available‑for‑sale	$ 51,548	$ 0