Disclosures About Fair Value - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Assets
Available-for-sale equity securities	$ 1,218
Available-for-sale debt securities	684
Carrying Value	1,902
Fair Value Measurements on a Recurring Basis
Assets
Available-for-sale equity securities	1,219
Available-for-sale debt securities	683
Carrying Value	1,902
Fair Value Measurements on a Recurring Basis | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Available-for-sale equity securities	975
Available-for-sale debt securities	683
Carrying Value	1,658
Fair Value Measurements on a Recurring Basis | Significant Other Observable Inputs (Level 2)
Assets
Available-for-sale equity securities	244
Available-for-sale debt securities	0
Carrying Value	244
Fair Value Measurements on a Recurring Basis | Significant Unobservable Inputs (Level 3)
Assets
Available-for-sale equity securities	0
Available-for-sale debt securities	0
Carrying Value	$ 0