Investment Securities - Schedule of Gross Unrealized Losses (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	$ 398,299	$ 444,968
Unrealized Loss, Less than 12 months	4,310	9,409
Fair Value, 12 months or more	48,317	22,199
Unrealized Loss, 12 months or more	1,471	810
Fair Value, Total	446,616	467,167
Unrealized Losses, Total	5,781	10,219
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	398,299	444,968
Unrealized Loss, Less than 12 months	4,310	9,409
Fair Value, 12 months or more	45,263	19,073
Unrealized Loss, 12 months or more	1,344	675
Fair Value, Total	443,562	464,041
Unrealized Losses, Total	5,654	10,084
Debt Securities | U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months		985
Unrealized Loss, Less than 12 months		13
Fair Value, 12 months or more	993
Unrealized Loss, 12 months or more	7
Fair Value, Total	993	985
Unrealized Losses, Total	7	13
Debt Securities | Mortgage-backed Securities - Residential
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	354,240	390,595
Unrealized Loss, Less than 12 months	3,800	7,230
Fair Value, 12 months or more	40,115	19,073
Unrealized Loss, 12 months or more	1,166	675
Fair Value, Total	394,355	409,668
Unrealized Losses, Total	4,966	7,905
Debt Securities | Municipals, Tax Exempt
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	35,240	43,132
Unrealized Loss, Less than 12 months	493	2,114
Fair Value, 12 months or more	4,155
Unrealized Loss, 12 months or more	171
Fair Value, Total	39,395	43,132
Unrealized Losses, Total	664	2,114
Debt Securities | Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	8,819	10,256
Unrealized Loss, Less than 12 months	17	52
Fair Value, Total	8,819	10,256
Unrealized Losses, Total	17	52
Equity Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, 12 months or more	3,054	3,126
Unrealized Loss, 12 months or more	127	135
Fair Value, Total	3,054	3,126
Unrealized Losses, Total	$ 127	$ 135