Long-Term incentive plan - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018
Description Of Conditions In Respect of Long Term Cash Incentives to eligible Participants				Historically, the long-term incentive plan (LTIP) was available for any employee who had been designated to be eligible to participate by the Compensation Committee of the Board of Directors. Annually, the LTIP provided for long-term cash incentive awards to eligible participants based on the Company’s performance over a three-year performance period.
Profit sharing, bonuses, and deferred compensation		$ 22,830	$ 1,365	$ 24,580	$ 3,005
Long Term Incentive Compensation Program [Member]
Payment of initial public offering cost	$ 10,483			10,483
Deferred Bonus [Member]
Other Deferred Compensation Arrangement Liability								$ 1,846
Profit sharing, bonuses, and deferred compensation		$ 9,921	$ 111	$ 10,000	$ 222
Chief Executive Officer [Member]
Increase In Fair Value Of Long Term Incentive Plan						12.00%	24.00%
Long Term Incentive Plan						3 years	3 years