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

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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.

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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.

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

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Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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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.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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No definition available.

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Cash, Cash Equivalents, and Available-for-sale Debt Securities

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No definition available.

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Cash, Cash Equivalents, and Available-for-sale Debt Securities, Amortized Cost

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No definition available.

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Marketable Securities - Schedule of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 65,256	$ 60,333	$ 52,204	$ 51,281
Schedule of Available-for-sale Securities [Line Items]
Unrealized Gains	0	0
Unrealized Losses	(114)	(69)
Cash and cash equivalents and available-for-sale securities, amortized cost	70,745	65,885
Cash and cash equivalents and available-for-sale securities	70,631	65,816
U.S. treasury debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,088	3,083
Unrealized Gains	0	0
Unrealized Losses	(8)	(8)
Aggregate Fair Value	3,080	3,075
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,827	13,350
Unrealized Gains	0	0
Unrealized Losses	(106)	(61)
Aggregate Fair Value	12,721	13,289
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	54,830	49,452
Cash and cash equivalents, aggregate fair value	54,830	49,452
Cash and cash equivalents \| Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	54,830	49,452
Cash and cash equivalents, aggregate fair value	54,830	49,452
Marketable securities \| U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,915	16,433
Unrealized Gains	0	0
Unrealized Losses	(114)	(69)
Aggregate Fair Value	$ 15,801	$ 16,364