Commitments and Contingencies (Schedule of Other Commitments) (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended							12 Months Ended													19 Months Ended	21 Months Ended
	Sep. 30, 2020	Aug. 31, 2020	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Dec. 31, 2017	Nov. 30, 2017	Dec. 31, 2016	Nov. 30, 2016	Dec. 31, 2015	Nov. 30, 2015	Dec. 31, 2014	Nov. 30, 2014	Dec. 31, 2013	Nov. 30, 2013	Nov. 30, 2012	Dec. 31, 2012
Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate																		0.00%
Antidumping Duties [Member] | Other Current Assets
Loss Contingencies [Line Items]
Contingent Receivable			$ 2,300
Antidumping Duties [Member] | Other Assets
Loss Contingencies [Line Items]
Contingent Receivable			1,300
Antidumping Duties [Member] | Other Current Liabilities
Loss Contingencies [Line Items]
Contingent Liability			200
Antidumping Duties [Member] | Other Long-Term Liabilities
Loss Contingencies [Line Items]
Contingent Liability			1,500
Antidumping Duties [Member] | First Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate								0.73%	5.92%														0.73%
Contingent Receivable			1,300								$ 1,300
Contingent Liability											$ 800
Antidumping Duties [Member] | Second Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																						3.30%
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate					3.92%	13.74%																3.92%
Contingent Liability			200	$ 4,100
Decrease in contingent liability				$ 3,900
Antidumping Duties [Member] | Third Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate	0.00%	17.37%																		0.00%
Contingent Receivable	$ 1,800		1,800
Contingent Liability	$ 4,700
Antidumping Duties [Member] | Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate																		0.00%
Antidumping Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate																0.00%
Antidumping Duties [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Contingent Receivable			500
Contingent Liability			1,500							$ 800
Antidumping Duties [Member] | Sixth Annual Review [Member] | Other Long-Term Liabilities
Loss Contingencies [Line Items]
Contingent Liability			$ 1,500
Antidumping Duties [Member] | Seventh Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate												0.00%
Loss Contingency Preliminary Purchase Price Of Anti dumping Duty Rate						0.0
Antidumping Duties [Member] | Minimum [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate							0.00%			0.00%
Antidumping Duties [Member] | Maximum [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate			42.57%				42.57%
Countervailing Duties [Member] | Other Current Assets
Loss Contingencies [Line Items]
Contingent Receivable			$ 70
Countervailing Duties [Member] | Other Assets
Loss Contingencies [Line Items]
Contingent Receivable			300
Countervailing Duties [Member] | Other Current Liabilities
Loss Contingencies [Line Items]
Contingent Liability			40
Countervailing Duties [Member] | Other Long-Term Liabilities
Loss Contingencies [Line Items]
Contingent Liability			1,700
Countervailing Duties [Member] | First and Second Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate																								1.50%
Contingent Receivable			200
Countervailing Duties [Member] | Third Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate																					1.50%
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate																					1.38%
Contingent Receivable			50
Countervailing Duties [Member] | Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate																			1.06%
Contingent Receivable			20
Countervailing Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Contingent Receivable			70
Countervailing Duties [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Contingent Liability			40							$ 400
Countervailing Duties [Member] | Seventh Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate				20.75%									20.75%
Contingent Liability			$ 1,700	$ 1,700
Countervailing Duties [Member] | Eighth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate											1.06%
Countervailing Duties [Member] | Minimum [Member] | First and Second Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate																								0.83%
Countervailing Duties [Member] | Minimum [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate								0.11%
Countervailing Duties [Member] | Minimum [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate							2.96%
Countervailing Duties [Member] | Maximum [Member] | First and Second Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate																								0.99%
Countervailing Duties [Member] | Maximum [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate								0.85%
Countervailing Duties [Member] | Maximum [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate							3.10%
Deposit One [Member] | Antidumping Duties [Member] | First Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																							6.78%
Deposit One [Member] | Antidumping Duties [Member] | Third Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																				3.30%
Deposit One [Member] | Antidumping Duties [Member] | Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																		5.92%
Deposit One [Member] | Antidumping Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																5.92%
Deposit One [Member] | Antidumping Duties [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate														17.37%
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate														42.57%
Deposit One [Member] | Countervailing Duties [Member] | Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate																			1.50%
Deposit One [Member] | Countervailing Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate																	0.83%
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate																	0.11%
Contingent Receivable								$ 70
Deposit One [Member] | Countervailing Duties [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate															0.99%
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate															3.10%
Deposit One [Member] | Countervailing Duties [Member] | Seventh Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate													1.38%
Deposit Two [Member] | Antidumping Duties [Member] | First Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																							3.30%
Deposit Two [Member] | Antidumping Duties [Member] | Third Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																				5.92%
Deposit Two [Member] | Antidumping Duties [Member] | Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																		13.74%
Deposit Two [Member] | Antidumping Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																13.74%
Deposit Two [Member] | Antidumping Duties [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate														0.00%
Loss Contingency Modified Purchase Price Of Antidumping Duty Rate														0.00%
Deposit Two [Member] | Countervailing Duties [Member] | Fourth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate																			0.83%
Deposit Two [Member] | Countervailing Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate																	0.99%
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate																	0.85%
Deposit Two [Member] | Countervailing Duties [Member] | Sixth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate															1.38%
Loss Contingency Modified Purchase Price Of Countervailing Duties Rate															2.96%
Deposit Two [Member] | Countervailing Duties [Member] | Seventh Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Countervailing Duties Rate													1.06%
Deposit Three [Member] | Antidumping Duties [Member] | Fifth Annual Review [Member]
Loss Contingencies [Line Items]
Loss Contingency Purchase Price Of Antidumping Duty Rate																17.37%