Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings from continuing operations before income taxes:
United States									$ 254,327	$ 344,614	$ 408,757
Foreign									59,459	61,767	60,458
Earnings from continuing operations before income taxes	$ 78,795	$ 94,343	$ 80,692	$ 59,956	$ 69,196	$ 131,698	$ 116,779	$ 88,708	313,786	406,381	469,215
Current tax expense (benefit) from continuing operations:
Federal									6,752	2,731	(1,836)
State									9,360	7,713	5,748
Foreign									6,442	6,411	5,272
Total									22,554	16,855	9,184
Deferred tax (benefit) expense from continuing operations:
Federal									(509,573)	106,513	135,585
State									7,985	16,259	20,111
Foreign									1,805	2,114	(1,654)
Total									(499,783)	124,886	154,042
(Benefit from) provision for income taxes from continuing operations									$ (477,229)	$ 141,741	$ 163,226