Investments in Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	$ 159,822	$ 88,072
Total Investments, Cost Basis	159,879	89,910
Total Investments, Accumulated Gross Unrealized Gains	42	388
Total Investments, Accumulated Gross Unrealized Losses	(99)	(89)
Total Investments	159,822	90,209
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Current	159,822	88,072
Other Assets
Schedule of Available-for-sale Securities [Line Items]
Total Investments, Noncurrent	0	2,137
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	57,382
Debt Securities, Accumulated Gross Unrealized Gains	32
Debt Securities, Accumulated Gross Unrealized Losses	(24)
Debt Securities	57,390
U.S. treasury securities \| Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	57,390
U.S. treasury securities \| Other Assets
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Noncurrent	0
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Cost Basis	102,497	88,161
Debt Securities, Accumulated Gross Unrealized Gains	10	0
Debt Securities, Accumulated Gross Unrealized Losses	(75)	(89)
Debt Securities	102,432	88,072
Corporate notes and bonds \| Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Current	102,432	88,072
Corporate notes and bonds \| Other Assets
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Noncurrent	$ 0	0
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Cost Basis		1,749
Equity Securities, Accumulated Gross Unrealized Gains		388
Equity Securities, Accumulated Gross Unrealized Losses		0
Equity securities		2,137
Equity securities \| Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Current		0
Equity securities \| Other Assets
Schedule of Available-for-sale Securities [Line Items]
Equity Securities, Noncurrent		$ 2,137

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt 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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