Selected Quarterly Financial Data - Unaudited - Summary of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quantifying Misstatement in Current Year Financial Statements, Amount		$ 200	$ 8,600
Revenues	$ 111,319	74,427	60,805	$ 40,886	$ 79,696	$ 35,975	$ 19,112	$ 14,352	$ 287,437	$ 149,135	$ 173,978
Gross Margin	42,891	30,502	20,277	15,029	29,948	12,538	6,301	2,216	108,699	51,003	42,610
Net Income (Loss)	24,614	14,932	(2,318)	$ 1,962	14,231	$ (492)	$ (7,061)	$ (9,926)	39,190	(3,248)	$ (87,182)
hear_FinancialInstrumentObligation	$ 7,848	$ 11,000	$ 11,200		$ 0				$ 7,848	$ 0
Earnings (Loss) Per Share
Basic (in dollars per share)	$ 1.73	$ 1.07	$ (0.17)	$ 0.16	$ 1.15	$ (0.04)	$ (0.57)	$ (0.81)	$ 2.90	$ (0.26)	$ (7.18)
Diluted (in dollars per share)	$ 1.33	$ 0.91	$ (0.17)	$ 0.16	$ 1.15	$ (0.04)	$ (0.57)	$ (0.81)	$ 2.74	$ (0.26)	$ (7.18)
Previously Reported [Member]
Net Income (Loss)		$ 14,700	$ 6,300
Earnings (Loss) Per Share
Diluted (in dollars per share)		$ 0.91	$ 0.40