Securities Available-for-Sale - Summary Of Expected Maturity Distribution Of Debt Securities Available-For-Sale, Other Than Mortgage-Backed Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized cost	$ 522,510	$ 505,834
Estimated fair value	515,121	$ 498,897
Other Than Mortgage Backed Securities
Amortized cost, Due in one year or less	0
Amortized cost, Due after one year through five years	58,174
Amortized cost, Due after five years through ten years	10,096
Amortized cost	68,270
Estimated fair value, Due in one year or less	0
Estimated fair value, Due after one year through five years	58,285
Estimated fair value, Due after five years through ten years	10,194
Estimated fair value	$ 68,479