Investments - Summary of Available-for-Sale Investments at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Cost	$ 28,364	$ 60,705
Gross Unrealized (Losses)	(17)	(137)
Gross Unrealized Gains		3
Estimated Fair Value	28,347	60,571
Estimated Fair Value - Short-term investments	28,347	33,574
Estimated Fair Value - Long-term investments		26,997
Short-term investments
Schedule of Available-for-sale Securities
Cost	28,364	33,598
Gross Unrealized (Losses)	(17)	(25)
Gross Unrealized Gains		1
Estimated Fair Value	28,347	33,574
Short-term investments \| Other cash equivalents – commercial paper
Schedule of Available-for-sale Securities
Cost		3,973
Gross Unrealized Gains		1
Estimated Fair Value		3,974
Short-term investments \| Corporate bonds
Schedule of Available-for-sale Securities
Cost	19,740	24,600
Gross Unrealized (Losses)	(11)	(25)
Estimated Fair Value	19,729	24,575
Short-term investments \| Municipal bonds
Schedule of Available-for-sale Securities
Cost	8,624	5,025
Gross Unrealized (Losses)	(6)
Estimated Fair Value	$ 8,618	5,025
Long-term investments
Schedule of Available-for-sale Securities
Cost		27,107
Gross Unrealized (Losses)		(112)
Gross Unrealized Gains		2
Estimated Fair Value		26,997
Long-term investments \| Corporate bonds
Schedule of Available-for-sale Securities
Cost		21,289
Gross Unrealized (Losses)		(103)
Estimated Fair Value		21,186
Long-term investments \| Municipal bonds
Schedule of Available-for-sale Securities
Cost		5,818
Gross Unrealized (Losses)		(9)
Gross Unrealized Gains		2
Estimated Fair Value		$ 5,811

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

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-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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