Investments (Details 1) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 1,504,898	$ 1,500,516
Available-for-sale Securities, Gross Unrealized Gain	41,528	27,774
Available-for-sale Securities, Gross Unrealized Loss	(6,745)	(33,545)
Securities available‑for‑sale	1,539,681	1,494,745
Government agency and government-sponsored enterprise pass through securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	537,969	691,944
Available-for-sale Securities, Gross Unrealized Gain	17,917	18,012
Available-for-sale Securities, Gross Unrealized Loss	(799)	(2,768)
Securities available‑for‑sale		707,188
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	280,820	197,069
Available-for-sale Securities, Gross Unrealized Gain	1,456	388
Available-for-sale Securities, Gross Unrealized Loss	(2,485)	(4,584)
Securities available‑for‑sale		192,873
Covered private label collateralized mortgage obligation [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	27,830	30,502
Available-for-sale Securities, Gross Unrealized Gain	7,568	7,552
Available-for-sale Securities, Gross Unrealized Loss	(89)	150
Securities available‑for‑sale		37,904
Other Private Label Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	12,563	0
Available-for-sale Securities, Gross Unrealized Gain	35	0
Available-for-sale Securities, Gross Unrealized Loss	(5)	0
Securities available‑for‑sale		0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	110,032	84,119
Available-for-sale Securities, Gross Unrealized Gain	2,139	71
Available-for-sale Securities, Gross Unrealized Loss	(28)	(1,483)
Securities available‑for‑sale		82,707
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	473,426	459,182
Available-for-sale Securities, Gross Unrealized Gain	12,212	1,749
Available-for-sale Securities, Gross Unrealized Loss	(3,211)	(24,273)
Securities available‑for‑sale		436,658
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	36,214	10,046
Available-for-sale Securities, Gross Unrealized Gain	168	0
Available-for-sale Securities, Gross Unrealized Loss	0	(174)
Securities available‑for‑sale		9,872
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	26,044	27,654
Available-for-sale Securities, Gross Unrealized Gain	33	2
Available-for-sale Securities, Gross Unrealized Loss	(128)	(113)
Securities available‑for‑sale		$ 27,543