Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	$ 416,863	$ 372,498
Held to Maturity, Fair Value, Total	414,470	369,881
Available for Sale, Amortized Cost, Total	960,220
Available for Sale, Fair Value, Total	955,804	950,503
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	6,248
Available for Sale, Fair Value, Due in less than one year	6,473
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	3,607
Available for Sale, Amortized Cost, Due after one year through five years	42,448
Available for Sale, Fair Value, Due after one year through five years	42,616
Held for Investment, Amortized Cost, Due after five years through ten years	36,923
Held for Investment, Fair Value, Due after five years through ten years	37,219
Available for Sale, Amortized Cost, Due after five years through ten years	256,306
Available for Sale, Fair Value, Due after five years through ten years	257,449
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	13,170
Available for Sale, Fair Value, Due after ten years	13,376
Held to Maturity, Amortized Cost, Total	40,523
Held to Maturity, Fair Value, Total	40,826
Available for Sale, Amortized Cost, Total	318,172
Available for Sale, Fair Value, Total	319,914
Mortgage-backed securities of U.S. Government Sponsored Entities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	172,261
Held to Maturity, Fair Value, Total	171,615	159,402
Available for Sale, Amortized Cost, Total	318,771
Available for Sale, Fair Value, Total	316,356	283,488
Collateralized Mortgage Obligations Of US Government Sponsored Entities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	181,279
Held to Maturity, Fair Value, Total	178,569	144,964
Available for Sale, Amortized Cost, Total	235,466
Available for Sale, Fair Value, Total	231,044	234,054
Commercial mortgage backed securities of U.S. Government Sponsored Entities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	17,463
Held to Maturity, Fair Value, Total	18,167	17,534
Available for Sale, Amortized Cost, Total	16,210
Available for Sale, Fair Value, Total	16,341	22,545
Private mortgage backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	0
Held to Maturity, Fair Value, Total	0	6,318
Available for Sale, Amortized Cost, Total	18,056
Available for Sale, Fair Value, Total	18,440	31,989
Private collateralized mortgage obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	5,337
Held to Maturity, Fair Value, Total	5,293
Available for Sale, Amortized Cost, Total	47,045
Available for Sale, Fair Value, Total	47,365	67,289
Corporate and other debt securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost, Total	0
Held to Maturity, Fair Value, Total	0
Available for Sale, Amortized Cost, Total	6,500
Available for Sale, Fair Value, Total	$ 6,344	$ 73,861