Income Taxes - Reconciliation Between U.S. Federal Statutory Tax Rate and Effective Tax Rate (Details)	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Reconciliation Between U.S. Federal Statutory Tax Rate and Effective Tax Rate
Provision for income taxes at U.S. federal statutory tax rate	35.00%	21.00%	31.60%	35.00%
State and local taxes (net of federal tax benefit)		4.60%	4.80%	3.60%
Revaluation of federal deferred tax liability from TCJA		0.00%	(371.60%)	0.00%
Tax rate differential from tax loss carryback		(2.80%)	0.00%	0.00%
Adjustment for prior year provision to return differences		(1.40%)	0.40%	(2.20%)
Effect of state tax law changes		(1.30%)	(0.10%)	1.50%
Other, net		(1.50%)	(1.70%)	(3.20%)
Effective tax rate		18.60%	(336.60%)	34.70%