Income Taxes (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Net deferred tax liabilities	$ 204,518,000		$ 204,518,000	$ 166,600,000
Deferred tax assets, net, current				11,800,000
Deferred tax liabilities, net, non-current				178,355,000
Valuation allowance, methodologies and assumptions			In assessing the ability to realize the deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which these temporary differences become deductible. Management considers the projected future taxable income and prudent and feasible tax planning strategies in making this assessment.
Net operating loss carryforwards	54,900,000		$ 54,900,000	$ 34,900,000
U.S. corporate tax rate, percent			35.00%	35.00%	35.00%
Change in enacted tax rate, non-cash tax benefit (in dollars)	120,100,000		$ 120,100,000
Provision for U.S. income taxes on unremitted foreign earnings	0		0
Unrecognized tax benefits	8,100,000		8,100,000	$ 0	$ 0	$ 0
Subsequent Event [Member]
Income Taxes [Line Items]
U.S. corporate tax rate, percent		21.00%
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	12,300,000		$ 12,300,000	9,000,000
State [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Net operating loss carryforwards, expiration date			Dec. 31, 2022
State [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Net operating loss carryforwards, expiration date			Dec. 31, 2037
Foreign [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	38,400,000		$ 38,400,000	22,700,000
Foreign [Member] | Earliest Tax Year [Member] | Canada [Member]
Income Taxes [Line Items]
Net operating loss carryforwards, expiration date			Jan. 01, 2033
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 200,000		$ 200,000	$ 500,000
Federal [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Net operating loss carryforwards, expiration date			Jan. 01, 2022