Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Basic Net Income Per Share
Net income	$ 31,798	$ 69,217	$ 13,071	$ 88,923	$ 73,961	$ 44,862	$ 50,127	$ 90,066	$ 203,009	$ 259,016	$ 112,170
Weighted average shares - basic									45,179	44,911	44,153
Net income per share - basic	$ 0.71	$ 1.53	$ 0.29	$ 1.97	$ 1.64	$ 1.00	$ 1.11	$ 2.02	$ 4.49	$ 5.77	$ 2.54
Diluted Net Income Per Share
Net income	$ 31,798	$ 69,217	$ 13,071	$ 88,923	$ 73,961	$ 44,862	$ 50,127	$ 90,066	$ 203,009	$ 259,016	$ 112,170
Weighted average shares - basic									45,179	44,911	44,153
Effect of dilutive securities									637	1,240	1,696
Weighted average shares - diluted									45,816	46,151	45,849
Net income per share - diluted	$ 0.70	$ 1.51	$ 0.28	$ 1.93	$ 1.60	$ 0.97	$ 1.09	$ 1.95	$ 4.43	$ 5.61	$ 2.45