Business Combination - Additional Information (Detail)						3 Months Ended								9 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Jan. 01, 2017	Sep. 26, 2016 USD ($)	Apr. 14, 2016 USD ($) shares	Jun. 10, 2014 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2016 SEK	Apr. 14, 2016 SEK SEK / shares
Business Acquisition [Line Items]
Business acquisition deferred payment consideration						$ 5,700,000				$ 0				$ 5,700,000	$ 5,700,000	$ 0	$ 0		SEK 50,620,000
Minimum lender required proceeds from issuance of private placement offer				$ 12,000,000
Noncontrolling interest						$ 279,000				0				$ 279,000	$ 279,000	0
Price per share of Allenex used to determine fair value of non controlling interest | $ / shares						$ 2.70								$ 2.70	$ 2.70
Total revenue						$ 10,859,000	$ 12,475,000	$ 10,735,000	$ 6,562,000	6,648,000	$ 7,151,000	$ 7,129,000	$ 7,216,000		$ 40,631,000	28,144,000	27,306,000
Net loss						15,483,000	$ 3,764,000	$ 10,470,000	$ 9,752,000	4,761,000	$ 3,489,000	$ 3,185,000	$ 2,272,000		39,469,000	13,707,000	(781,000)
Goodwill acquired in business combination, estimated fair value						13,839,000				12,005,000				$ 13,839,000	13,839,000	12,005,000
Accumulated amortization of intangible asset						1,721,000								1,721,000	1,721,000
Stock-based compensation															$ 1,998,000	1,341,000	535,000
Public Offering [Member]
Business Acquisition [Line Items]
Proceeds from majority shareholders in exchange of equity securities			$ 9,000,000
Allenex [Member]
Business Acquisition [Line Items]
Percentage of share acquired				98.30%																98.30%
Total purchase price combination of cash and common stock				$ 34,100,000
Cash distribution to acquire business, gross				$ 26,900,000
Common stock, shares issue | shares				1,375,029
Common stock value				$ 7,200,000
Business acquisition deferred payment consideration				5,700,000																SEK 50,620,000
Escrow deposit				$ 8,000,000
Business acquisition deferred payment extended date															Jul. 01, 2017
Business acquisition deferred purchase price consideration carrying value						5,400,000								5,400,000	$ 5,400,000
Business acquisition of related cost expenses															4,300,000
Percentage of non controlling interest				1.70%																1.70%
Noncontrolling interest				$ 600,000																SEK 5,100,000
Price per share of Allenex used to determine fair value of non controlling interest | SEK / shares																				SEK 2.48
Total revenue														10,700,000
Net loss														$ 17,900,000
Goodwill acquired in business combination, estimated fair value				$ 16,922,000
Allenex [Member] | In-process technology [Member]
Business Acquisition [Line Items]
Estimated useful life of identified intangible asset				15 years
Allenex [Member] | Six-Month Bridge Loan [Member]
Business Acquisition [Line Items]
Business acquisition of debt financing cost															2,100,000	2,100,000
Allenex [Member] | Public Offering [Member]
Business Acquisition [Line Items]
Proceeds from majority shareholders in exchange of equity securities			$ 9,000,000
Allenex [Member] | Scenario Forecast [Member]
Business Acquisition [Line Items]
Proceeds from majority shareholders in exchange of equity securities	$ 20,000,000
Allenex [Member] | Pro Forma [Member]
Business Acquisition [Line Items]
Business acquisition of related cost expenses															$ 4,300,000	4,300,000
ImmuMetrix, Inc. [Member]
Business Acquisition [Line Items]
Total purchase price combination of cash and common stock					$ 17,200,000
Cash distribution to acquire business, gross					$ 600,000
Common stock, shares issue | shares					911,364
Business acquisition of related cost expenses																	1,700,000
Acquisition date															Jun. 10, 2014
Milestone description															the milestone will be achieved if the Company completes 2,500 commercial tests involving the measurement of dd-cfDNA in organ transplant recipients in the United States no later than six years after the closing date of the acquisition.
Estimated fair value of share issued for acquisition					$ 14,200,000
Contingent consideration milestone measurement period for organ transplant recipients														6 years
Contingent consideration					2,300,000	$ 500,000				900,000				$ 500,000	$ 500,000	900,000
Goodwill acquired in business combination, estimated fair value					12,000,000
Stock-based compensation																	200,000
Business combination pro forma removal (addition) in income tax benefit																	1,500,000	$ 1,500,000
ImmuMetrix, Inc. [Member] | In-process technology [Member]
Business Acquisition [Line Items]
Assets acquired in business combination, estimated fair value					$ 6,700,000
Accumulated amortization of intangible asset										$ 0						$ 0	$ 0
Estimated useful life of identified intangible asset															15 years
ImmuMetrix, Inc. [Member] | Series G convertible preferred stock [Member]
Business Acquisition [Line Items]
Common stock, shares issue | shares					227,845
ImmuMetrix, Inc. [Member] | Series G convertible preferred stock [Member] | Company’s assumption of IMX outstanding stock options [Member]
Business Acquisition [Line Items]
Common stock, shares issue | shares					23,229
Estimated fair value of share issued for acquisition					$ 369,000
Majority Shareholder [Member] | Allenex [Member]
Business Acquisition [Line Items]
Escrow deposit				$ 8,000,000
Majority Shareholder [Member] | Allenex [Member] | Scenario Forecast [Member]
Business Acquisition [Line Items]
Business acquisition deferred payment consideration	$ 6,200,000
Majority Shareholder [Member] | Subsequent Event [Member] | Allenex [Member]
Business Acquisition [Line Items]
Percentage of accruing interest		10.00%
Maximum [Member] | Allenex [Member]
Business Acquisition [Line Items]
Business acquisition deferred payment date															Mar. 31, 2017