Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as trading, available-for-sale, or held-to-maturity. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Marketable Securities and Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Estimated fair values	$ 86,508,000		$ 86,508,000		$ 99,710,000
Other-than-temporary impairment loss	0	$ 0	0	$ 0
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities, realized gains and losses	0	$ 0	0	$ 0
Long-term marketable securities
Fair Value Disclosures [Abstract]
Estimated fair values	$ 29,809,000		$ 29,809,000		$ 30,967,000
Long-term marketable securities \| Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities term			1 year
Long-term marketable securities \| Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities term			3 years