Investments Summary of Assets, Liabilities and Results of Operations for Significant Unconsolidated Joint Ventures (Details) - Significant Unconsolidated Joint Ventures - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Current assets	$ 476,460	$ 503,043
Noncurrent assets	1,159,866	1,041,519
Total assets	1,636,326	1,544,562
Current liabilities	191,971	133,670
Noncurrent liabilities	422,769	405,662
Total liabilities	614,740	539,332
Net sales	829,590	687,561	$ 590,980
Gross profit	456,518	353,577	267,241
Income before income taxes	332,632	267,805	189,016
Net income	$ 225,791	$ 184,777	$ 126,872