Securities (Unrealized Loss NOT deemed to be OTTI) (Details) $ in Thousands	Mar. 31, 2018 USD ($) holding	Dec. 31, 2017 USD ($) holding
Summary of gross unrealized losses and fair value of investments
No of holdings | holding	204	163
Fair value, less than 12 months	$ 674,680	$ 475,739
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months	(13,617)	(3,465)
Fair value, 12 months or longer	176,263	193,298
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months	(8,898)	(6,919)
Fair value, Total	850,943	669,037
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss	$ (22,515)	$ (10,384)
U. S. Government Agency Securities [Member]
Summary of gross unrealized losses and fair value of investments
No of holdings | holding	6	4
Fair value, less than 12 months	$ 34,943	$ 24,343
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months	(535)	(131)
Fair value, 12 months or longer	0	0
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months		0
Fair value, Total	34,943	24,343
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss	$ (535)	$ (131)
Agency mortgage-backed securities
Summary of gross unrealized losses and fair value of investments
No of holdings | holding	140	84
Fair value, less than 12 months	$ 338,326	$ 235,411
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months	(6,624)	(1,493)
Fair value, 12 months or longer	14,205	14,886
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months	(568)	(310)
Fair value, Total	352,531	250,297
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss	$ (7,192)	$ (1,803)
Agency Collateralized Mortgage Obligations [Member]
Summary of gross unrealized losses and fair value of investments
No of holdings | holding	51	42
Fair value, less than 12 months	$ 244,572	$ 178,142
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months	(5,384)	(1,579)
Fair value, 12 months or longer	150,834	159,506
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months	(7,633)	(5,572)
Fair value, Total	395,406	337,648
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss	$ (13,017)	$ (7,151)
Pooled trust preferred securities issued by banks and insurers
Summary of gross unrealized losses and fair value of investments
No of holdings | holding	1	1
Fair value, less than 12 months	$ 0	$ 0
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months	0	0
Fair value, 12 months or longer	1,655	1,640
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months	(518)	(539)
Fair value, Total	1,655	1,640
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss	$ (518)	$ (539)
Equity securities
Summary of gross unrealized losses and fair value of investments
No of holdings | holding		28
Fair value, less than 12 months		$ 3,290
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months		(39)
Fair value, 12 months or longer		7,619
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months		(403)
Fair value, Total		10,909
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss		$ (442)
Small Business Administration Pooled Securities [Member]
Summary of gross unrealized losses and fair value of investments
No of holdings | holding	6	4
Fair value, less than 12 months	$ 56,839	$ 34,553
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for less than 12 months	(1,074)	(223)
Fair value, 12 months or longer	9,569	9,647
Unrealized loss position for available for sale and held to maturity securities in a continuous loss position for more than 12 months	(179)	(95)
Fair value, Total	66,408	44,200
Available for Sale and Held to Maturity Securities Continuous Unrealized Loss Position Aggregate Loss	$ (1,253)	$ (318)