Operations and Summary of Significant Accounting Policies - PP&E and Other Misc Disclosures (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) vote / shares series bank	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
High end of the range of the required percentage voting interest held to account for investments with the equity method of accounting	50.00%
Allowance for Doubtful Accounts
Percentage reserved for accounts receivable due from customers in deteriorating financial condition	100.00%
Number of banks where demand deposit or money market accounts are held by the company | bank	17
Fair Value of Financial Instruments
United States Treasury securities and money market funds included in cash equivalents	$ 200	$ 5,300
Contingent Consideration for acquisition	$ 0	$ 1,314	$ 0
Depreciation and Amortization
Number of series by which the Board may issue authorized and unissued preferred stock, minimum | series	1
Voting rights per common share | vote / shares	1
Minimum | Buildings and site improvements
Depreciation and Amortization
Estimated useful life	15 years
Maximum | Buildings and site improvements
Depreciation and Amortization
Estimated useful life	45 years