CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation adjustment, tax expense	$ 16	$ 37	$ (1)	$ 12
Unrealized holding losses on marketable securities arising during the period, tax	0	0	0	20
Change in unfunded SERP liability, tax	$ (11)	$ (25)	$ (22)	$ (51)
Class A Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 0.06	$ 0.06	$ 0.12	$ 0.12
Class B Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared (in dollars per share)	$ 0.07	$ 0.07	$ 0.14	$ 0.14

Aggregate dividends declared during the period for each share of common stock outstanding.

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount of tax expense (benefit), after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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