Income Taxes (Significant Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Timing of expense recognition	$ 22,730	$ 36,055
Net operating losses	8,590	10,140
Other, net	15,618	33,507
Deferred tax assets	46,938	79,702
Valuation Allowance	(381)	(460)
Net deferred tax assets	46,557	79,242
Deferred tax liabilities:
Intangible assets, due primarily to purchase accounting	(30,019)	(34,679)
Fixed assets, due primarily to purchase accounting	(73,833)	(107,081)
Construction contract accounting	(17,539)	(12,564)
Joint ventures	(11,343)	(29,609)
Other	(22,263)	(24,970)
Deferred tax liabilities	(154,997)	(208,903)
Net deferred tax liabilities	(108,440)	(129,661)
Net Deferred Tax Liabilities
Deferred tax asset	64	1,346
Deferred tax liability	(108,504)	(131,007)
Net deferred tax liabilities	$ (108,440)	$ (129,661)