Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Total	$ 400,647	$ 416,863
Held for Investment, Fair Value, Total	391,867	414,470
Available for Sale, Amortized Cost, Total	998,241
Available for Sale, Fair Value, Total	982,958	949,460
Collateralized Loan Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Due in less than one year	0
Held for Investment, Fair Value, Due in less than one year	0
Available for Sale Amortized Cost, Due in less than one year	7,635
Available for Sale, Fair Value, Due in less than one year	7,849
Held for Investment, Amortized Cost, Due after one year through five years	3,600
Held for Investment, Fair Value, Due after one year through five years	3,602
Available for Sale, Amortized Cost, Due after one year through five years	34,651
Available for Sale, Fair Value, Due after one year through five years	34,673
Held for Investment, Amortized Cost, Due after five years through ten years	32,000
Held for Investment, Fair Value, Due after five years through ten years	32,209
Available for Sale, Amortized Cost, Due after five years through ten years	254,328
Available for Sale, Fair Value, Due after five years through ten years	255,151
Held for Investment, Amortized Cost, Due after ten years	0
Held for Investment, Fair Value, Due after ten years	0
Available for Sale, Amortized Cost, Due after ten years	13,144
Available for Sale, Fair Value, Due after ten years	12,916
Held for Investment, Amortized Cost, Total	35,600
Held for Investment, Fair Value, Total	35,811
Available for Sale, Amortized Cost, Total	309,758
Available for Sale, Fair Value, Total	310,589
Mortgage-backed securities of U.S. Government Sponsored Entities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Total	168,462
Held for Investment, Fair Value, Total	164,938	171,615
Available for Sale, Amortized Cost, Total	328,521
Available for Sale, Fair Value, Total	319,885	316,356
Collateralized Mortgage Obligations Of US Government Sponsored Entities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Total	174,080
Held for Investment, Fair Value, Total	168,239	178,569
Available for Sale, Amortized Cost, Total	281,335
Available for Sale, Fair Value, Total	273,278	231,044
Commercial mortgage backed securities of U.S. Government Sponsored Entities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Total	17,487
Held for Investment, Fair Value, Total	17,899	18,167
Available for Sale, Amortized Cost, Total	16,183
Available for Sale, Fair Value, Total	16,041	16,341
Private mortgage backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Total	0
Held for Investment, Fair Value, Total	0
Available for Sale, Amortized Cost, Total	18,070
Available for Sale, Fair Value, Total	18,449	18,440
Private collateralized mortgage obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held for Investment, Amortized Cost, Total	5,018
Held for Investment, Fair Value, Total	4,980	5,293
Available for Sale, Amortized Cost, Total	44,374
Available for Sale, Fair Value, Total	$ 44,716	$ 47,365