Investment Securities - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available for sale:
Total	$ 875,805	$ 786,783
Unrealized Gain	2,874	6,161
Unrealized Loss	(15,436)	(5,515)
Investment securities available-for-sale, at fair value	863,243	787,429
Held to maturity:
Amortized Cost	24,559	18,291
Unrealized Gain	0	0
Unrealized Loss	(644)	(209)
Estimated Fair Value	23,915	18,082
Total investment securities
Amortized Cost	900,364	805,074
Unrealized Gain	2,874	6,161
Unrealized Loss	(16,080)	(5,724)
Estimated Fair Value	887,158	805,511
Agency
Available for sale:
Total	44,208	47,051
Unrealized Gain	60	236
Unrealized Loss	(104)	(78)
Investment securities available-for-sale, at fair value	44,164	47,209
Corporate
Available for sale:
Total	103,671	78,155
Unrealized Gain	1,084	1,585
Unrealized Loss	(349)	(194)
Investment securities available-for-sale, at fair value	104,406	79,546
Municipal bonds
Available for sale:
Total	225,201	228,929
Unrealized Gain	1,522	3,942
Unrealized Loss	(3,066)	(743)
Investment securities available-for-sale, at fair value	223,657	232,128
Collateralized mortgage obligation: residential
Available for sale:
Total	32,223	33,984
Unrealized Gain	97	132
Unrealized Loss	(611)	(335)
Investment securities available-for-sale, at fair value	31,709	33,781
Mortgage-backed securities: residential
Available for sale:
Total	470,502	398,664
Unrealized Gain	111	266
Unrealized Loss	(11,306)	(4,165)
Investment securities available-for-sale, at fair value	459,307	394,765
Held to maturity:
Amortized Cost	23,434	17,153
Unrealized Gain	0	0
Unrealized Loss	(644)	(209)
Estimated Fair Value	22,790	16,944
Other
Held to maturity:
Amortized Cost	1,125	1,138
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	$ 1,125	$ 1,138