Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended		21 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
(Provision for) benefit from income taxes		$ 2,172	$ 850	$ (18,472)	$ 5,256
Effective income tax benefit rate		(8.80%)	15.50%	26.80%	23.10%
Increase (decrease) in gross unrecognized tax benefits		$ 1,100		$ 3,500
Cumulative effect adjustment related to unrecognized excess tax benefits on share based compensation		58,700		58,700				$ 58,700
U.S. statutory federal income tax rate, percent								35.00%
Additional income tax expense		$ 12,200		$ 12,200
Scenario Forecast [Member]
Income Tax Contingency [Line Items]
U.S. statutory federal income tax rate, percent	21.00%					21.00%
U.S. statutory federal income tax rate, percent							31.60%