Reportable Operating Segments - Reconciliation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Reconciliations of total assets from reportable segments to the condensed consolidated balance sheets
Cash and cash equivalents	$ 493,002	$ 291,764	$ 296,428	$ 245,956
Deferred tax assets	33,612	44,708
Total assets	1,530,963	1,191,780
Reportable segments
Reconciliations of total assets from reportable segments to the condensed consolidated balance sheets
Total assets	790,231	606,058
Unallocated overhead costs
Reconciliations of total assets from reportable segments to the condensed consolidated balance sheets
Cash and cash equivalents	493,002	291,764
Deferred tax assets	33,612	44,708
Other unallocated corporate assets	$ 214,118	$ 249,250