Stock-Based Compensation (Stock-Based Compensation Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Stock-based compensation expense related to:
Stock-based compensation expense	$ 30,027	$ 28,961	$ 27,053
Tax benefit	(10,624)	(10,392)	(9,338)
Stock-based compensation expense, net of tax	19,403	18,569	17,715
Stock Options [Member]
Stock-based compensation expense related to:
Stock-based compensation expense	25,935	24,892	22,969
Employee Stock Purchase Plan [Member]
Stock-based compensation expense related to:
Stock-based compensation expense	$ 4,092	$ 4,069	$ 4,084