Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]
Balance at Dec. 31, 2015	$ 49,425	$ 328	$ 62,163	$ (13,066)
Balance (in shares) at Dec. 31, 2015		32,804,617
Sale of common stock	48,356	$ 74	48,282	0
Sale of common stock (in shares)		7,392,856
Issuance of common stock upon exercise of stock options and warrants	2,704	$ 13	2,691	0
Issuance of common stock upon exercise of stock options and warrants (in shares)		1,251,199
Excess tax benefits from exercise of stock options	189	$ 0	189	0
Issuance of common stock for services	105	$ 0	105	0
Issuance of common stock for services (in shares)		17,148
Value of share-based arrangements	601	$ 0	601	0
Value of share-based arrangements (in shares)		0
Net income	10,637	$ 0	0	10,637
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	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	$ 0	17	0
Issuance of common stock upon exercise of stock options and warrants (in shares)		5,000
Issuance of common stock for services	348	$ 2	346	0
Issuance of common stock for services (in shares)		199,291
Value of share-based arrangements	1,054	$ 0	1,054	0
Value of share-based arrangements (in shares)		0
Net income	(55,659)	$ 0	0	(55,659)
Balance at Dec. 31, 2018	$ 69,213	$ 426	$ 115,719	$ (46,932)
Balance (in shares) at Dec. 31, 2018		42,602,431