Basis of Presentation and Summary of Significant Accounting Policies (Investment Categories) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Summary of investment categories
Amortized cost	$ 110,383	$ 120,758
Gross unrealized gains	2,065	1,564
Gross unrealized losses	(44)	(26)
Estimated fair value	112,404	122,296
Bank deposits
Summary of investment categories
Amortized cost	55,847	40,715
Gross unrealized gains	12	19
Gross unrealized losses	(9)	0
Estimated fair value	55,850	40,734
Corporate bonds
Summary of investment categories
Amortized cost	30,043	11,031
Gross unrealized gains	2	0
Gross unrealized losses	(24)	(5)
Estimated fair value	30,021	11,026
Commercial paper
Summary of investment categories
Amortized cost	13,948	33,074
Gross unrealized gains	0	2
Gross unrealized losses	(3)	(9)
Estimated fair value	13,945	33,067
Agency bonds
Summary of investment categories
Amortized cost	0	7,294
Gross unrealized gains	0	1
Gross unrealized losses	0	0
Estimated fair value	0	7,295
U.S Government Bonds
Summary of investment categories
Amortized cost	8,474	7,508
Gross unrealized gains	0	0
Gross unrealized losses	(8)	(1)
Estimated fair value	8,466	7,507
Municipal Bonds
Summary of investment categories
Amortized cost	1,784	19,624
Gross unrealized gains	0	0
Gross unrealized losses	0	(11)
Estimated fair value	1,784	19,613
Corporate equity securities
Summary of investment categories
Amortized cost	287	1,512
Gross unrealized gains	2,051	1,542
Gross unrealized losses	0	0
Estimated fair value	$ 2,338	$ 3,054

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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