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Summary of Significant Accounting Policies (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) Institution	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Aug. 31, 2013 USD ($)
Concentration of Credit Risk and Others Risks and Uncertainties [Abstract]
Number of financial institutions holding company's cash | Institution	2
Prepaid Expenses [Abstract]
Prepayment of facility lease for corporate promotional and marketing purposes	$ 4,000
Lease term	10 years
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Adjusted Cost	$ 5,544	$ 3,609	$ 3,135	$ 6,627
Adjusted Cost	2,626		2,617
Unrealized Gains	0		0
Unrealized Losses	0		(1)
Fair Value	2,626		2,616
Adjusted Cost	6,127		4,589
Fair Value	6,127		4,588
Investments Available for Sale	2,626		2,616
Cash [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Adjusted Cost	3,501		1,972
Fair Value	3,501		1,972
Cash and Cash Equivalents	3,501		1,972
Mutual Funds [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Adjusted Cost	1,177		616
Unrealized Gains	0		0
Unrealized Losses	0		0
Fair Value	1,177		616
Investments Available for Sale	1,177		616
U.S. Government Securities [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Adjusted Cost	80
Unrealized Gains	0
Unrealized Losses	0
Fair Value	80
Investments Available for Sale	80
U.S. Agency Securities [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Adjusted Cost	1,369		2,001
Unrealized Gains	0		0
Unrealized Losses	0		(1)
Fair Value	1,369		2,000
Investments Available for Sale	1,369		2,000
Recurring [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Fair Value	5,544		3,135
Fair Value	583		1,453
Cash and Cash Equivalents	5,544		3,135
Investments Available for Sale	583		1,453
Recurring [Member] | Cash [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Fair Value	3,501		1,972
Cash and Cash Equivalents	3,501		1,972
Recurring [Member] | Level 1 [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Fair Value	2,043		1,163
Fair Value	583		1,453
Cash and Cash Equivalents	2,043		1,163
Investments Available for Sale	583		1,453
Recurring [Member] | Level 1 [Member] | Mutual Funds [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Fair Value	1,177		616
Fair Value	0
Cash and Cash Equivalents	1,177		616
Investments Available for Sale	0
Recurring [Member] | Level 1 [Member] | U.S. Government Securities [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Fair Value	0
Fair Value	80
Cash and Cash Equivalents	0
Investments Available for Sale	80
Recurring [Member] | Level 1 [Member] | U.S. Agency Securities [Member]
Cash and available-for-sale securities adjusted cost, gross unrealized gains, gross unrealized losses and fair value by significant investment category [Abstract]
Fair Value	866		547
Fair Value	503		1,453
Cash and Cash Equivalents	866		547
Investments Available for Sale	$ 503		1,453
August 2013 Contract [Member]
Deferred Revenue [Abstract]
Term of contract	4 years
Deferred revenue					$ 10,000
Revenue recognized		$ 375
ASU 2014-09 [Member]
Deferred Revenue [Abstract]
Revenue recognized			2,500
ASU 2014-09 [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments			(2,500)
ASU 2014-09 [Member] | Deferred Revenue [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments			$ (2,500)

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