CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
NET INCOME	$ 141,384	$ 139,598	$ 166,075	$ 172,434
Derivative instruments:
Net unrealized gain (loss), net of tax benefit (expense) of $(26) and $105 for three months ended June 30, 2014 and 2013 and of $(624) and $67 for six months ended June 30, 2014 and 2013	40	(160)	(381)	(102)
Reclassification of net realized loss, net of tax benefit of $1,261 and $2,824 for three months ended June 30, 2014 and 2013 and $2,584 and $6,124 for six months ended June 30, 2014 and 2013	1,955	4,322	5,070	9,375
Pension and other postretirement benefits activity, net of tax benefit (expense) of $845 and $449 for three months ended June 30, 2014 and 2013 and $128 and $(182) for six months ended June 30, 2014 and 2013	(1,310)	(688)	(853)	278
Total other comprehensive income	685	3,474	3,836	9,551
COMPREHENSIVE INCOME	142,069	143,072	169,911	181,985
Less: Comprehensive income attributable to noncontrolling interests	8,926	8,391	17,851	16,783
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 133,143	$ 134,681	$ 152,060	$ 165,202