Disclosures About Fair Value - Fair Value of Assets and Liabilities on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Available-for-sale equity securities	$ 60,380	$ 20,689
Total	131,260	25,071
Fair Value, Measurements, Recurring
Assets
Available-for-sale equity securities	60,380	20,689
Available-for-sale debt securities	70,880	4,382
Total	131,260	25,071
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Available-for-sale equity securities	60,136	12,545
Available-for-sale debt securities	70,880	4,382
Total	131,016	16,927
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Available-for-sale equity securities	244	8,144
Available-for-sale debt securities
Total	244	8,144
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Available-for-sale equity securities
Available-for-sale debt securities