Investment Securities - Schedule of Amortized Cost and Fair Value by Contractual Maturity of Debt Securities (Details) - Municipal securities $ in Thousands	Dec. 31, 2017 USD ($)
Schedule Of Debt Securities [Line Items]
Within 1 year, amortized cost	$ 3,730
1-5 years, amortized cost	10,665
Amortized Cost	14,395
Within 1 year, fair value	3,728
1-5 years, fair value	10,693
Fair Value	$ 14,421
Within 1 year, weighted average yield	1.64%
1-5 years, weighted average yield	2.66%
Weighted Average Yield	2.40%