Cash Equivalents and Investments - Tabular Disclosure - Total (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2017	Dec. 31, 2016
Cash Equivalents and Investments
Total, Amortized Cost	$ 236,439	$ 268,236
Total, Unrealized Gain	1	14
Total, Unrealized Losses	(115)	(32)
Total, Fair Value	$ 236,325	$ 268,218
US Treasury obligations
Cash Equivalents and Investments
Average Maturity	321 days	298 days
Available-for-sale, Amortized Cost	$ 180,084	$ 216,167
Available-for-sale, Unrealized Gain		14
Available-for-sale, Unrealized Losses	(115)	(32)
Available-for-sale, Fair Value	179,969	216,149
Money market fund
Cash Equivalents and Investments
Cash equivalents, Amortized Cost	50,364	52,069
Cash equivalents, Fair Value	50,364	$ 52,069
Government agency securities
Cash Equivalents and Investments
Cash equivalents, Amortized Cost	5,991
Cash equivalents, Unrealized Gain	1
Cash equivalents, Fair Value	$ 5,992

Represents the average maturity of available-for-sale security.

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- Definition

Represents the cost of cash equivalents and cost of debt 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

No definition available.

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- Definition

Unrealized gain in on cash equivalents.

+ References

No definition available.

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- Definition

Represents the fair value of cash equivalents and amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

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- Definition

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

+ References

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- Definition

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

+ References

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- Definition

This item represents the cost of debt 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 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount of debt securities categorized neither as held-to-maturity nor trading.

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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-Paragraph 1
-Subparagraph (SX 210.5-02.1)
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-URI http://asc.fasb.org/extlink&oid=6507016

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- References

No definition available.

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- Definition

The increase (decrease), resulting in a gain, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

+ References

No definition available.

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- Definition

The increase (decrease), resulting in a loss, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period.

+ References

No definition available.

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