Disclosures About Fair Value - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Available-for-sale equity securities	$ 1,257
Available-for-sale equity securities		$ 1,218
Debt securities: corporate bonds	497	684
Carrying Value		1,902
Fair Value Measurements on a Recurring Basis
Assets
Available-for-sale equity securities	1,257
Available-for-sale equity securities		1,219
Debt securities: corporate bonds	497	683
Carrying Value	1,754	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 equity securities		975
Debt securities: corporate bonds	497	683
Carrying Value	1,472	1,658
Fair Value Measurements on a Recurring Basis | Significant Other Observable Inputs (Level 2)
Assets
Available-for-sale equity securities	282
Available-for-sale equity securities		244
Debt securities: corporate bonds
Carrying Value	282	244
Fair Value Measurements on a Recurring Basis | Significant Unobservable Inputs (Level 3)
Assets
Available-for-sale equity securities
Available-for-sale equity securities
Debt securities: corporate bonds
Carrying Value