Goodwill Schedule of Goodwill Allocated to Reporting Segments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)
Goodwill [Roll Forward]
Goodwill before impairment, at beginning of period	$ 1,096,660
Accumulated impairment losses, at beginning of period	(628,538)
Goodwill, net, at beginning of period	468,122
Effect of change in exchange rates	7,750
Goodwill before impairment, at end of period	1,117,133
Accumulated impairment losses, at end of period	(641,261)
Goodwill, net, at end of period	475,872
Electricity Operating Segment [Member]
Goodwill [Roll Forward]
Goodwill before impairment, at beginning of period	414,910
Accumulated impairment losses, at beginning of period	(362,177)
Goodwill, net, at beginning of period	52,733
Effect of change in exchange rates	600
Goodwill before impairment, at end of period	422,011
Accumulated impairment losses, at end of period	(368,678)
Goodwill, net, at end of period	53,333
Gas Operating Segment [Member]
Goodwill [Roll Forward]
Goodwill before impairment, at beginning of period	331,436
Accumulated impairment losses, at beginning of period	0
Goodwill, net, at beginning of period	331,436
Effect of change in exchange rates	5,756
Goodwill before impairment, at end of period	337,192
Accumulated impairment losses, at end of period	0
Goodwill, net, at end of period	337,192
Water Operating Segment [Member]
Goodwill [Roll Forward]
Goodwill before impairment, at beginning of period	350,314
Accumulated impairment losses, at beginning of period	(266,361)
Goodwill, net, at beginning of period	83,953
Effect of change in exchange rates	1,394
Goodwill before impairment, at end of period	357,930
Accumulated impairment losses, at end of period	(272,583)
Goodwill, net, at end of period	$ 85,347