Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pretax losses	$ 11,159	$ 6,049
Change in tax rate effect on deferred tax liability			$ 16,200
Transition tax			3,700
Increase in global tax rate	0.60%
Accumulated other comprehensive loss	$ (4,579)		(4,366)
Retained earnings	283,538		$ 274,562	$ 274,836
Accounting Standards Update 2018-02
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accumulated other comprehensive loss	(350)
Retained earnings	350
Europe | Solar Racking Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pretax losses	$ 900