Business Combinations - Acquisition of Cloverleaf (Details) - USD ($) $ in Thousands	12 Months Ended	20 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	May 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Goodwill	$ 794,335	$ 794,335	$ 318,483		$ 186,095	$ 188,169
Goodwill	1,115
Cloverleaf
Assets
Land	60,494	60,494		$ 59,363
Land		1,131
Buildings and improvements	668,151	668,151		687,821
Buildings and improvements		(19,670)
Machinery and equipment	145,647	145,647		144,825
Machinery and equipment		822
Assets under construction	16,974	16,974		20,968
Assets under construction		(3,994)
Operating lease right-of-use assets	1,254	1,254		1,254
Operating lease right-of-use assets		0
Cash and cash equivalents	4,332	4,332		4,332
Cash and cash equivalents		0
Restricted cash	526	526		0
Restricted cash		526
Accounts receivable	21,578	21,578		21,358
Accounts receivable		220
Goodwill	126,096	126,096		107,643
Goodwill		18,453
Acquired identifiable intangibles:
Other assets	7,052	7,052		18,720
Other assets		(11,668)
Total assets	1,304,073	1,304,073		1,309,645
Total assets		(5,572)
Liabilities
Accounts payable and accrued expenses	43,503	43,503		30,905
Accounts payable and accrued expenses		12,598
Notes payable	3,878	3,878		17,179
Notes payable		(13,301)
Operating lease obligations	1,254	1,254		1,254
Operating lease obligations		0
Unearned revenue	3,536	3,536		3,536
Unearned revenue		0
Pension and postretirement benefits	0	0		2,020
Pension and postretirement benefits		(2,020)
Deferred tax liability	9,024	9,024		9,063
Deferred tax liability		(39)
Total liabilities	61,195	61,195		63,957
Total liabilities		(2,762)
Total consideration, including common shares issued and deferred consideration	1,242,878	1,242,878		1,245,688
Total consideration for Cloverleaf acquisition		(2,810)
Customer relationships | Cloverleaf
Acquired identifiable intangibles:
Acquired identifiable intangibles	250,346	250,346		241,738
Acquired identifiable intangibles		8,608
Trade names and trademarks | Cloverleaf
Acquired identifiable intangibles:
Acquired identifiable intangibles	$ 1,623	1,623		$ 1,623
Acquired identifiable intangibles		$ 0