Accounts Payable and Accrued Expenses (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Trade payables	$ 85,038,000	$ 93,501,000
Accrued workers’ compensation liabilities	30,585,000	32,041,000
Accrued payroll	12,238,000	11,727,000
Accrued bonus	17,335,000	16,382,000
Accrued vacation and long service leave	14,988,000	15,718,000
Accrued health benefits	10,987,000	9,332,000
Accrued property taxes	14,376,000	15,067,000
Accrued utilities	6,274,000	6,004,000
Taxes payable	290,000	785,000
Dividends payable	28,540,000	0
Other accrued expenses	32,429,000	40,702,000
Accounts payable and accrued expenses	$ 253,080,000	$ 241,259,000