Commitments and Contingencies - Summary of accrued short- and long-term insurance liabilities (Details) - Insurance Claims [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accrued short- and long-term insurance liabilities
Balance at beginning of period	$ 54,039	$ 45,363	$ 42,584
Net increases in reserves	45,419	31,193	22,938
Net payments made	(32,654)	(22,517)	(20,159)
Balance at end of period	$ 66,804	$ 54,039	$ 45,363