Fair Value of Financial Instruments (Cash and Cash Equivalents, Available-for-sale Securities, Restricted Cash Reconciliation) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	$ 222,454	$ 166,656
Unrealized Gains	6	37
Unrealized Losses	(217)	(27)
Fair value	222,243	166,666
Cash and Cash Equivalents
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	91,696	76,504
Unrealized Gains	2	0
Unrealized Losses	0	0
Fair value	91,698	76,504
Cash and Cash Equivalents \| Cash
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	61,372	36,024
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	61,372	36,024
Cash and Cash Equivalents \| Money market funds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	3,980	39,180
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair value	3,980	39,180
Cash and Cash Equivalents \| U.S. government agencies
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	8,999	300
Unrealized Gains	1	0
Unrealized Losses	0	0
Fair value	9,000	300
Cash and Cash Equivalents \| Commercial paper
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	17,345	1,000
Unrealized Gains	1	0
Unrealized Losses	0	0
Fair value	17,346	1,000
Short-term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	87,317	50,716
Unrealized Gains	4	10
Unrealized Losses	(53)	(12)
Fair value	87,268	50,714
Short-term Investments \| U.S. government agencies
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	64,422	33,280
Unrealized Gains	3	3
Unrealized Losses	(40)	(6)
Fair value	64,385	33,277
Short-term Investments \| Commercial paper
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	10,447	4,998
Unrealized Gains	1	1
Unrealized Losses	0	0
Fair value	10,448	4,999
Short-term Investments \| Corporate bonds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	12,448	12,438
Unrealized Gains	0	6
Unrealized Losses	(13)	(6)
Fair value	12,435	12,438
Long-Term Investments
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	43,441	39,436
Unrealized Gains	0	27
Unrealized Losses	(164)	(15)
Fair value	43,277	39,448
Long-Term Investments \| U.S. government agencies
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	32,683	20,243
Unrealized Gains	0	22
Unrealized Losses	(142)	(10)
Fair value	32,541	20,255
Long-Term Investments \| Corporate bonds
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	3,751	3,101
Unrealized Gains	0	0
Unrealized Losses	(4)	(2)
Fair value	3,747	3,099
Long-Term Investments \| Asset-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Amortized cost, total	7,007	16,092
Unrealized Gains	0	5
Unrealized Losses	(18)	(3)
Fair value	$ 6,989	$ 16,094

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26626-111562

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