Investments (Details 1) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	$ 1,670,791	$ 1,522,871
Available-for-sale Securities, Gross Unrealized Gain	38,924	47,908
Available-for-sale Securities, Gross Unrealized Loss	(11,557)	(3,602)
Securities available‑for‑sale	1,698,158	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	411,842	515,902
Available-for-sale Securities, Gross Unrealized Gain	15,282	20,142
Available-for-sale Securities, Gross Unrealized Loss	(250)	(372)
Securities available‑for‑sale	426,874	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	262,222	275,513
Available-for-sale Securities, Gross Unrealized Gain	4,443	3,513
Available-for-sale Securities, Gross Unrealized Loss	(766)	(1,080)
Securities available‑for‑sale	265,899	277,946
Covered private label collateralized mortgage obligation [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	25,835	26,889
Available-for-sale Securities, Gross Unrealized Gain	6,573	7,153
Available-for-sale Securities, Gross Unrealized Loss	(85)	(95)
Securities available‑for‑sale	32,323	33,947
Other Private Label Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	8,025	10,961
Available-for-sale Securities, Gross Unrealized Gain	43	46
Available-for-sale Securities, Gross Unrealized Loss	(43)	(93)
Securities available‑for‑sale	8,025	10,914
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	720,835	521,499
Available-for-sale Securities, Gross Unrealized Gain	10,358	15,899
Available-for-sale Securities, Gross Unrealized Loss	(9,637)	(1,282)
Securities available‑for‑sale	721,556	536,116
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	47,438	110,074
Available-for-sale Securities, Gross Unrealized Gain	343	597
Available-for-sale Securities, Gross Unrealized Loss	(371)	(562)
Securities available‑for‑sale	47,410	110,109
Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	133,128	0
Available-for-sale Securities, Gross Unrealized Gain	1,067	0
Available-for-sale Securities, Gross Unrealized Loss	(288)	0
Securities available‑for‑sale	133,907	0
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	36,267	36,232
Available-for-sale Securities, Gross Unrealized Gain	813	525
Available-for-sale Securities, Gross Unrealized Loss	0	0
Securities available‑for‑sale	37,080	36,757
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities available-for-sale	25,199	25,801
Available-for-sale Securities, Gross Unrealized Gain	2	33
Available-for-sale Securities, Gross Unrealized Loss	(117)	(118)
Securities available‑for‑sale	$ 25,084	$ 25,716