Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2016	$ 112,017	$ 415	$ 114,032	$ (2,430)
Balance (in shares) at Dec. 31, 2016		41,465,820
Issuance of common stock upon exercise of stock options and warrants	807	$ 12	795	0
Issuance of common stock upon exercise of stock options and warrants (in shares)		1,207,729
Tax withholdings related to net share settlements of stock option awards	(2,026)	$ (3)	(2,023)	0
Tax withholdings related to net share settlements of stock option awards (in shares)		(281,645)
Issuance of common stock for services	47	$ 0	47	0
Issuance of common stock for services (in shares)		6,236
Value of share-based arrangements	1,451	$ 0	1,451	0
Value of share-based arrangements (in shares)		0
Net income (loss)	11,157	$ 0	0	11,157
Balance at Dec. 31, 2017	123,453	$ 424	114,302	8,727
Balance (in shares) at Dec. 31, 2017		42,398,140
Issuance of common stock upon exercise of stock options and warrants	17		17	0
Issuance of common stock upon exercise of stock options and warrants (in shares)		5,000
Value of share-based arrangements	212		212	0
Net income (loss)	(33,672)	0	0	(33,672)
Balance at Jun. 30, 2018	$ 90,010	$ 424	$ 114,531	$ (24,945)
Balance (in shares) at Jun. 30, 2018		42,403,140