Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended
	Mar. 02, 2016	Mar. 06, 2015	Jan. 13, 2015	Dec. 18, 2014	Mar. 31, 2016	Mar. 31, 2015
Class Of Stock [Line Items]
Cash dividends declared per share to shareholders					$ 0.25	$ 0.40
Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash distribution declaration date					Mar. 02, 2016
Cash distributions to unit holders, date of record					Mar. 31, 2016
Dividends Payable, date declared					Mar. 02, 2016
Dividends payable date of record					Mar. 31, 2016
Cash dividends declared per share to shareholders	$ 0.25
Cash distribution and dividend paid date					Apr. 21, 2016
Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash distribution declaration date					Mar. 06, 2015
Cash distributions to unit holders, date of record					Mar. 31, 2015
Dividends Payable, date declared					Mar. 06, 2015
Dividends payable date of record					Mar. 31, 2015
Cash dividends declared per share to shareholders		$ 0.14
Cash distribution and dividend paid date					Apr. 23, 2015
Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash distribution declaration date					Jan. 13, 2015
Cash distributions to unit holders, date of record					Jan. 20, 2015
Dividends Payable, date declared					Jan. 13, 2015
Dividends payable date of record					Jan. 20, 2015
Cash dividends declared per share to shareholders			$ 0.26
Cash distribution and dividend paid date					Jan. 29, 2015
Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash distribution declaration date					Dec. 18, 2014
Cash distributions to unit holders, date of record					Dec. 18, 2014
Dividends Payable, date declared					Dec. 18, 2014
Dividends payable date of record					Dec. 18, 2014
Cash dividends declared per share to shareholders				$ 0.31
Cash distribution and dividend paid date					Jan. 16, 2015
Accumulated Deficit | Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders	$ 10.9
Accumulated Deficit | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders		$ 6.1
Accumulated Deficit | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders			$ 9.0
Accumulated Deficit | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash dividends declared to shareholders				$ 10.8
InfraREIT, L.L.C. | Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit	$ 0.25
Cash distribution to unit holders	$ 15.2
InfraREIT, L.L.C. | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit		$ 0.14
Cash distribution to unit holders		$ 8.5
InfraREIT, L.L.C. | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit			$ 0.26
Cash distribution to unit holders			$ 11.7
InfraREIT, L.L.C. | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit				$ 0.31
Cash distribution to unit holders				$ 14.1
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders	$ 10.9
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders		$ 6.1
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders			$ 9.0
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash dividends declared to shareholders				$ 10.8