Marketable Securities and Fair Value Measurements - Schedule of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Marketable securities and fair value measurements
Amortized Cost	$ 86,556	$ 99,761
Gross Unrealized Gains	34	24
Gross Unrealized Losses	(82)	(75)
Estimated Fair Value	86,508	99,710
Investment securities
Marketable securities and fair value measurements
Amortized Cost	56,719	63,135
Gross Unrealized Gains	12	7
Gross Unrealized Losses	(32)	(39)
Estimated Fair Value	56,699	63,103
Commercial paper
Marketable securities and fair value measurements
Amortized Cost		5,641
Gross Unrealized Gains		1
Gross Unrealized Losses		(2)
Estimated Fair Value		5,640
Investment securities
Marketable securities and fair value measurements
Amortized Cost	29,837	30,985
Gross Unrealized Gains	22	16
Gross Unrealized Losses	(50)	(34)
Estimated Fair Value	$ 29,809	$ 30,967

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt 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=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt 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)
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 25
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ 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)
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