Stockholders' Equity Stockholders' Equity (Change in Retained Earnings) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			$ 743,815
Net income	156,706	140,897	160,374	144,682
Repurchase of common stock			(13,305)
Balance, end of period	$ 890,884		$ 890,884