Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Summary Of Investments (Details)

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Fair Value Measurements - Summary Of Investments (Details) - Common stock investments, available for sale - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 7,585 $ 3,409
Gross unrealized gains in Accumulated OCI 5,075 1,313
Gross unrealized losses in Accumulated OCI (199) (194)
Fair value $ 12,461 $ 4,528