Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Business Segment Information
Revenues.	$ 329,651	$ 335,107	$ 328,501	$ 319,024	$ 327,631	$ 314,681	$ 305,520	$ 300,031	$ 1,312,283	$ 1,247,863	$ 1,020,669
Long-lived assets, net	528,646				491,848				528,646	491,848
United States of America
Business Segment Information
Revenues.									912,063	843,791	628,147
Long-lived assets, net	272,422				216,279				272,422	216,279
United Kingdom
Business Segment Information
Revenues.									182,365	209,232	195,547
India
Business Segment Information
Long-lived assets, net	238,367				251,722				238,367	251,722
Rest Of World
Business Segment Information
Revenues.									217,855	194,840	$ 196,975
Long-lived assets, net	$ 17,857				$ 23,847				$ 17,857	$ 23,847