Acquisitions RARE Acquisition (Details) AUD in Thousands, $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Sep. 30, 2016 AUD	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2017 AUD	Sep. 30, 2017 USD ($)		Mar. 31, 2016 USD ($)	Oct. 21, 2015 USD ($)
Business Acquisition [Line Items]
Line of Credit Facility, Fair Value of Amount Outstanding				$ 40,000
RARE Infrastructure, Ltd [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability									$ 25,000
Assets Under Management									$ 6,800,000
Noncontrolling Interest, Ownership Percentage by Parent									75.00%
Payments to Acquire Businesses, Gross	AUD 296,000	$ 213,739
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High					AUD 106,000	$ 83,174	[1]
Business Combination, Contingent Consideration, Liability				17,444		2,180		$ 27,145	$ 25,000
Contingent consideration fair value adjustments			$ (15,264)
Business Combination, Contingent Consideration, Liability, Current				7,791		0
Business Combination, Contingent Consideration, Liability, Noncurrent				9,653		$ 2,180
RARE Management Team [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners									15.00%
Outside Investors
Business Acquisition [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners									10.00%
Change in Input Assumptions [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition [Line Items]
Contingent consideration fair value adjustments			(15,250)	(10,000)
Other changes in Fair Value [Member] | RARE Infrastructure, Ltd [Member]
Business Acquisition [Line Items]
Contingent consideration fair value adjustments			$ (14)	$ 299

[1] Using the applicable exchange rate as of September 30, 2017, for amounts denominated in currencies other than the U.S. dollar.