Overview and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounting Policies [Abstract]
Initial offering period		December 2011
Changes in revenue from adjustments of prior period deferred revenue	$ 1.9		$ 2.2
Revenue and income from operations	$ 2.3		$ 3.6
Impact on reported earnings per share	$ 0		$ 0.01