Transition period (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Mar. 31, 2020	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net sales	$ 74,712	$ 80,760	$ 67,615	$ 59,764	$ 66,141	$ 78,571	$ 63,889	$ 59,055	$ 65,920	$ 282,851	$ 267,435	$ 269,888
Cost of sales					25,650				25,712	101,728	104,694	105,163
Gross profit	48,064	52,520	43,348	37,191	40,491	46,919	38,969	36,645	40,208	181,123	162,741	164,725
Selling, general, and administrative expenses					37,324				36,234	157,155	136,579	131,446
Restructuring (income) loss					22,176				0	(5,982)	0	0
Operating income (loss)					(19,009)				3,974	29,950	26,162	33,279
Other income (expense), net					(315)				(888)	426	(390)	(2,035)
Interest expense, net					(1,849)				(1,963)	(6,307)	(7,816)	(8,775)
Income (loss) before provision for income taxes					(21,173)				1,123	24,069	17,956	22,469
Income tax (provision) benefit					3,259				(433)	(6,185)	(2,431)	11,006
Net income (loss)	$ (341)	$ 8,002	$ 6,517	$ 3,706	(17,914)	$ 9,672	$ 3,915	$ 1,248	690	17,884	15,525	33,475
Comprehensive income (loss)					$ (17,914)				$ 690	$ 17,884	$ 15,525	$ 33,475
Basic (in USD per share)	$ (0.01)	$ 0.16	$ 0.13	$ 0.08	$ (0.37)	$ 0.20	$ 0.08	$ 0.03	$ 0.01	$ 0.37	$ 0.33	$ 0.74
Diluted (in USD per share)	$ (0.01)	$ 0.16	$ 0.13	$ 0.07	$ (0.37)	$ 0.20	$ 0.08	$ 0.03	$ 0.01	$ 0.35	$ 0.32	$ 0.68
Basic (in shares)					48,022,926				46,435,560	48,498,813	46,828,798	45,358,452
Diluted (in shares)					48,022,926				49,302,771	50,817,143	49,268,616	49,374,758
Cash flows from operating activities:
Net income (loss)	$ (341)	$ 8,002	$ 6,517	$ 3,706	$ (17,914)	$ 9,672	$ 3,915	$ 1,248	$ 690	$ 17,884	$ 15,525	$ 33,475
Depreciation and amortization					7,544				4,288	22,843	17,861	14,521
Restructuring (income) loss					22,176				0	(5,982)	0	0
Stock-based compensation expense					3,683				3,640	15,488	16,821	13,474
Amortization of debt issuance costs and discount on debt					190				199	747	792	810
Deferred income taxes					(3,433)				735	2,443	(939)	(13,434)
Other, net					242				142	873	476	1,728
Accounts receivable					4,215				12,771	2,504	7,649	(8,001)
Inventories					2,561				951	(435)	16,338	6,718
Prepaid expenses and other assets					(1,732)				(1,498)	(6,500)	(8,484)	(11,200)
Accounts payable and accrued expenses					(6,021)				(16,891)	5,962	(10,251)	(25,483)
Other liabilities					(3,295)				3	(11,514)	(206)	(230)
Net cash provided by operating activities					8,216				5,030	44,313	55,582	12,378
Cash flows from investing activities:
Purchase of property and equipment					(3,400)				(2,667)	(9,422)	(8,872)	(7,544)
Net cash used in investing activities					(3,400)				(2,667)	(35,345)	(8,872)	(10,419)
Cash flows from financing activities:
Proceeds from revolving line of credit					0				2,000	0	2,000	25,900
Repayment of revolving line of credit					0				(2,000)	0	(2,000)	(25,900)
Repayment of long-term debt					(2,063)				(2,063)	(9,488)	(8,250)	(8,250)
Cash received from issuance of common stock					115				212	1,488	3,176	1,978
Other, net					(199)				(97)	(771)	(490)	(404)
Net cash used in financing activities					(2,147)				(1,948)	(16,675)	(5,564)	(7,195)
Net (decrease) increase in cash and cash equivalents					2,669				415	(7,707)	41,146	(5,236)
Cash and cash equivalents - beginning of period				$ 53,874	51,205			$ 10,474	10,059	53,874	10,059	15,295
Cash and cash equivalents - end of period	$ 46,167				$ 53,874	$ 51,205			$ 10,474	$ 46,167	$ 51,205	$ 10,059