Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	$ 866,840	$ 880,946
Unrealized Gains	(23,311)	(24,296)
Unrealized Losses	(4,315)	(8,189)
Securities available-for-sale	885,836	897,053
US Government Agencies Debt Securities [Member]
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	11,059	1,411
Unrealized Gains	(61)	(56)
Unrealized Losses	0	0
Securities available-for-sale	11,120	1,467
Mortgage Backed Securities - Residential
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	188,184	180,673
Unrealized Gains	(6,391)	(7,593)
Unrealized Losses	(235)	(330)
Securities available-for-sale	194,340	187,936
Mortgage Backed Securities - Commercial
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	10	17
Unrealized Gains	0	0
Unrealized Losses	0	0
Securities available-for-sale	10	17
Collateralized Mortgage Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	453,593	489,765
Unrealized Gains	(4,019)	(2,513)
Unrealized Losses	(3,703)	(7,623)
Securities available-for-sale	453,909	484,655
State and Municipal Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	204,279	198,875
Unrealized Gains	(7,438)	(9,019)
Unrealized Losses	(377)	(219)
Securities available-for-sale	211,340	207,675
Collateralized Debt Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	9,715	10,205
Unrealized Gains	(5,402)	(5,115)
Unrealized Losses	0	(17)
Securities available-for-sale	$ 15,117	$ 15,303