Basis of Presentation (Investment Categories) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Summary of investment categories
Amortized cost	$ 62,705	$ 3,440
Gross unrealized gains	11,277	4,954
Gross unrealized losses	(11)	0
Estimated fair value	73,971	8,394
Bank deposits
Summary of investment categories
Amortized cost	38,174
Gross unrealized gains	3
Gross unrealized losses	(3)
Estimated fair value	38,174
Corporate bonds
Summary of investment categories
Amortized cost	5,115
Gross unrealized gains	0
Gross unrealized losses	(5)
Estimated fair value	5,110
Commercial paper
Summary of investment categories
Amortized cost	3,498
Gross unrealized gains	0
Gross unrealized losses	0
Estimated fair value	3,498
Asset backed securities
Summary of investment categories
Amortized cost	13,330
Gross unrealized gains	0
Gross unrealized losses	(3)
Estimated fair value	13,327
Corporate equity securities
Summary of investment categories
Amortized cost	1,988	2,179
Gross unrealized gains	11,274	4,954
Gross unrealized losses	0	0
Estimated fair value	13,262	7,133
Restricted investments
Summary of investment categories
Amortized cost	600	1,261
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	$ 600	$ 1,261

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

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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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