Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 350,715	$ 276,831	$ 181,222
Other Comprehensive Income (Loss):
Net unrealized gain (loss) on investments, net of taxes	1,228	407	(99)
Realized gain on investments	(651)	0	0
Realized (loss) gain on derivatives	0	(2,084)	5,007
Net unrealized gain (loss) on derivatives	1,063	(1,204)	(3,061)
Reclassification adjustment of derivatives and designated hedges into net income	(42)	1,531	2,798
Retirement liability adjustment	1,393	(167)	147
Total	2,991	(1,517)	4,792
Comprehensive Income	353,706	275,314	186,014
Comprehensive Income Attributable to Noncontrolling Interests	(15,441)	(37,898)	(6,870)
Comprehensive Income Adjusted for Noncontrolling Interests	$ 338,265	$ 237,416	$ 179,144