Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 82,347	$ 50	$ 12	$ 155,793	$ (73,508)
Balance, shares at Dec. 31, 2017		10	11,651
Exercise of stock options	914	$ 0	$ 0	914	0
Exercise of stock options, shares		0	72
Issuance of restricted common stock	0	$ 0	$ 0	0	0
Issuance of restricted common stock, shares		0	210
Forfeiture of restricted common stock	0	$ 0	$ 0	0	0
Forfeiture of restricted common stock, shares		0	(19)
Purchase and retirement of common stock	(1,120)	$ 0	$ 0	(1,120)	0
Purchase and retirement of common stock, shares		0	(38)
Stock-based compensation	3,573	$ 0	$ 0	3,573	0
Cumulative effect of the adoption of the new revenue standard, net of tax	139	0	0	0	139
Net loss	(16,150)	0	0	0	(16,150)
Balance at Jun. 30, 2018	69,703	$ 50	$ 12	159,160	(89,519)
Balance, shares at Jun. 30, 2018		10	11,876
Balance at Mar. 31, 2018	76,121	$ 50	$ 12	157,540	(81,481)
Balance, shares at Mar. 31, 2018		10	11,847
Exercise of stock options	354	$ 0	$ 0	354	0
Exercise of stock options, shares		0	26
Issuance of restricted common stock	0	$ 0	$ 0	0	0
Issuance of restricted common stock, shares		0	32
Forfeiture of restricted common stock	0	$ 0	$ 0	0	0
Forfeiture of restricted common stock, shares		0	(9)
Purchase and retirement of common stock	(592)	$ 0	$ 0	(592)	0
Purchase and retirement of common stock, shares		0	(20)
Stock-based compensation	1,858	$ 0	$ 0	1,858	0
Net loss	(8,038)	0	0	0	(8,038)
Balance at Jun. 30, 2018	69,703	$ 50	$ 12	159,160	(89,519)
Balance, shares at Jun. 30, 2018		10	11,876
Balance at Dec. 31, 2018	56,615	$ 50	$ 12	162,428	(105,875)
Balance, shares at Dec. 31, 2018		10	11,891
Issuance of common stock, net of issuance costs	19,615	$ 0	$ 0	19,615	0
Issuance of common stock, net of issuance costs, shares		0	336
Exercise of stock options	$ 293	$ 0	$ 0	293	0
Exercise of stock options, shares	23	0	23
Issuance of restricted common stock	$ 0	$ 0	$ 0	0	0
Issuance of restricted common stock, shares		0	273
Forfeiture of restricted common stock	0	$ 0	$ 0	0	0
Forfeiture of restricted common stock, shares		0	(46)
Purchase and retirement of common stock	(1,868)	$ 0	$ 0	(1,868)	0
Purchase and retirement of common stock, shares		0	(44)
Stock-based compensation	4,143	$ 0	$ 0	4,143	0
Net loss	(16,396)	0	0	0	(16,396)
Balance at Jun. 30, 2019	62,402	$ 50	$ 12	184,611	(122,271)
Balance, shares at Jun. 30, 2019		10	12,433
Balance at Mar. 31, 2019	49,843	$ 50	$ 12	164,119	(114,338)
Balance, shares at Mar. 31, 2019		10	12,135
Issuance of common stock, net of issuance costs	19,615	$ 0	$ 0	19,615	0
Issuance of common stock, net of issuance costs, shares		0	336
Exercise of stock options	$ 194	$ 0	$ 0	194	0
Exercise of stock options, shares	13	0	13
Issuance of restricted common stock	$ 0	$ 0	$ 0	0	0
Issuance of restricted common stock, shares		0	18
Forfeiture of restricted common stock	0	$ 0	$ 0	0	0
Forfeiture of restricted common stock, shares		0	(45)
Purchase and retirement of common stock	(1,382)	$ 0	$ 0	(1,382)	0
Purchase and retirement of common stock, shares		0	(24)
Stock-based compensation	2,065	$ 0	$ 0	2,065	0
Net loss	(7,933)	0	0	0	(7,933)
Balance at Jun. 30, 2019	$ 62,402	$ 50	$ 12	$ 184,611	$ (122,271)
Balance, shares at Jun. 30, 2019		10	12,433