Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Thousands	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Mar. 31, 2015	3	20,262
Balance at Mar. 31, 2015	$ 9,000	$ 20,000	$ 3,117,000	$ 72,343,000	$ (54,000)	$ 75,435,000
Issuance of restricted stock, net (in shares)		185
Issuance of restricted stock, net
Share based compensation			1,612,000			1,612,000
Dividends declared				(14,615,000)		(14,615,000)
Excess tax benefit related to stock compensation			142,000			142,000
Net income				20,567,000	20,567,000	20,567,000
Other comprehensive gain:
Net change in unrealized gain on short term investments					54,000	54,000
Total comprehensive income					20,621,000	20,621,000
Issuance of restricted stock, net (in shares)		185
Issuance of restricted stock, net
Share based compensation			1,612,000			1,612,000
Dividends declared				(14,615,000)		(14,615,000)
Net income				20,567,000	20,567,000	20,567,000
Balance (in shares) at Mar. 31, 2016	3	20,447
Balance at Mar. 31, 2016	$ 9,000	$ 20,000	4,871,000	78,295,000		83,195,000
Issuance of restricted stock, net (in shares)		79
Issuance of restricted stock, net		$ 1,000				1,000
Share based compensation			1,935,000			1,935,000
Dividends declared				(15,584,000)		(15,584,000)
Net income				23,819,000	23,819,000	23,819,000
Other comprehensive gain:
Net change in unrealized gain on short term investments						0
Total comprehensive income						23,819,000
Issuance of restricted stock, net (in shares)		79
Issuance of restricted stock, net		$ 1,000				1,000
Share based compensation			1,935,000			1,935,000
Dividends declared				(15,584,000)		(15,584,000)
Net income				23,819,000	23,819,000	23,819,000
Balance (in shares) at Mar. 31, 2017	3	20,526
Balance at Mar. 31, 2017	$ 9,000	$ 21,000	6,806,000	86,530,000		93,366,000
Issuance of restricted stock, net (in shares)		75
Issuance of restricted stock, net
Share based compensation			2,575,000			2,575,000
Dividends declared				(17,493,000)		(17,493,000)
Net income				37,283,000	37,283,000	37,283,000
Other comprehensive gain:
Net change in unrealized gain on short term investments						0
Total comprehensive income						37,283,000
Issuance of restricted stock, net (in shares)		75
Issuance of restricted stock, net
Share based compensation			2,575,000			2,575,000
Dividends declared				(17,493,000)		(17,493,000)
Net income				37,283,000	37,283,000	37,283,000
Balance (in shares) at Mar. 31, 2018	3	20,601
Balance at Mar. 31, 2018	$ 9,000	$ 21,000	$ 9,381,000	$ 106,320,000		$ 115,731,000