Revenue Recognition, Consolidaed Balance Sheet (Details) - USD ($)		Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016
Current assets [Abstract]
Cash and cash equivalents		$ 12,242,000	$ 13,049,000
Short-term investments		3,053,000	2,828,000
Accounts receivable - net		40,510,000	63,174,000
Inventory - net		187,342,000	161,210,000
Inventory unreturned		8,315,000	7,508,000
Contract assets (see Note 7)		16,542,000	15,614,000
Income tax receivable		9,416,000	7,796,000
Prepaid expenses and other current assets		13,148,000	11,491,000
Total current assets		290,568,000	282,670,000
Plant and equipment - net		28,026,000	28,322,000
Long-term core inventory - net			0
Long-term core inventory deposits			0
Long-term deferred income taxes		10,343,000	10,317,000
Long-term contract assets		207,792,000	205,998,000
Goodwill		2,551,000	2,551,000	$ 2,551,000	$ 2,551,000
Intangible assets - net		3,567,000	3,766,000
Other assets		6,406,000	7,392,000
TOTAL ASSETS		549,253,000	541,016,000
Current liabilities [Abstract]
Accounts payable		86,633,000	73,273,000
Accrued liabilities		9,358,000	11,799,000
Customer finished goods returns accrual		16,438,000	17,805,000
Accrued core payment			0
Contract liabilities		32,083,000	32,603,000
Revolving loan		45,406,000	54,000,000
Other current liabilities		6,159,000	4,471,000
Current portion of term loan		2,749,000	3,068,000
Total current liabilities		198,826,000	197,019,000
Term loan, less current portion		26,954,000	13,913,000
Long-term accrued core payment			0
Long-term deferred income taxes		216,000	226,000
Long-term contract liabilities		45,666,000	48,183,000
Other liabilities		6,853,000	5,957,000
Total liabilities		278,515,000	265,298,000
Commitments and contingencies
Shareholders' equity [Abstract]
Preferred stock		0	0
Common stock; par value $.01 per share, 50,000,000 shares authorized; 18,893,102 shares issued and outstanding at March 31, 2018		189,000	189,000
Additional paid-in capital		214,358,000	213,609,000
Retained earnings		63,080,000	67,348,000
Accumulated other comprehensive loss		(6,889,000)	(5,428,000)
Total shareholders' equity		270,738,000	275,718,000
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY		$ 549,253,000	$ 541,016,000
Balance Sheet Parenthetical Information [Abstract]
Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01
Preferred stock, authorized (in shares)		5,000,000	5,000,000
Preferred stock, issued (in shares)		0	0
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Common stock, authorized (in shares)		50,000,000	50,000,000
Common stock, issued (in shares)		18,916,108	18,893,102
Common stock, outstanding (in shares)		18,916,108	18,893,102
Series A Junior Participating Preferred Stock [Member]
Shareholders' equity [Abstract]
Preferred stock		$ 0	$ 0
Balance Sheet Parenthetical Information [Abstract]
Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01
Preferred stock, authorized (in shares)		20,000	20,000
Preferred stock, issued (in shares)		0	0
As Previously Reported [Member] | ASC 606 [Member]
Current assets [Abstract]
Cash and cash equivalents			$ 13,049,000
Short-term investments			2,828,000
Accounts receivable - net			15,738,000
Inventory - net			76,275,000
Inventory unreturned			7,508,000
Contract assets (see Note 7)			0
Income tax receivable			7,796,000
Prepaid expenses and other current assets			11,491,000
Total current assets			134,685,000
Plant and equipment - net			28,322,000
Long-term core inventory - net			301,656,000
Long-term core inventory deposits			5,569,000
Long-term deferred income taxes			10,556,000
Long-term contract assets			0
Goodwill			2,551,000
Intangible assets - net			3,766,000
Other assets			7,392,000
TOTAL ASSETS			494,497,000
Current liabilities [Abstract]
Accounts payable			73,273,000
Accrued liabilities			11,799,000
Customer finished goods returns accrual			17,805,000
Accrued core payment			16,536,000
Contract liabilities			0
Revolving loan			54,000,000
Other current liabilities			4,471,000
Current portion of term loan			3,068,000
Total current liabilities			180,952,000
Term loan, less current portion			13,913,000
Long-term accrued core payment			18,473,000
Long-term deferred income taxes			226,000
Long-term contract liabilities			0
Other liabilities			5,957,000
Total liabilities			219,521,000
Commitments and contingencies
Shareholders' equity [Abstract]
Preferred stock			0
Common stock; par value $.01 per share, 50,000,000 shares authorized; 18,893,102 shares issued and outstanding at March 31, 2018			189,000
Additional paid-in capital			213,609,000
Retained earnings			66,606,000
Accumulated other comprehensive loss			(5,428,000)
Total shareholders' equity			274,976,000
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY			494,497,000
Adoption of ASU 2014-09 [Member] | ASC 606 [Member]
Current assets [Abstract]
Cash and cash equivalents			0
Short-term investments			0
Accounts receivable - net			47,436,000
Inventory - net			84,935,000
Inventory unreturned			0
Contract assets (see Note 7)			15,614,000
Income tax receivable			0
Prepaid expenses and other current assets			0
Total current assets			147,985,000
Plant and equipment - net			0
Long-term core inventory - net			(301,656,000)
Long-term core inventory deposits	[1]		(5,569,000)
Long-term deferred income taxes			(239,000)
Long-term contract assets			205,998,000
Goodwill			0
Intangible assets - net			0
Other assets			0
TOTAL ASSETS			46,519,000
Current liabilities [Abstract]
Accounts payable			0
Accrued liabilities			0
Customer finished goods returns accrual			0
Accrued core payment			(16,536,000)
Contract liabilities			32,603,000
Revolving loan			0
Other current liabilities			0
Current portion of term loan			0
Total current liabilities			16,067,000
Term loan, less current portion			0
Long-term accrued core payment			(18,473,000)
Long-term deferred income taxes			0
Long-term contract liabilities			48,183,000
Other liabilities			0
Total liabilities			45,777,000
Commitments and contingencies
Shareholders' equity [Abstract]
Preferred stock			0
Common stock; par value $.01 per share, 50,000,000 shares authorized; 18,893,102 shares issued and outstanding at March 31, 2018			0
Additional paid-in capital			0
Retained earnings			742,000			$ 345,000
Accumulated other comprehensive loss			0
Total shareholders' equity			742,000
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY			$ 46,519,000

[1] Long-term core inventory deposits of $5,569,000 have been reclassified to long-term contract assets in the consolidated balance sheet at March 31, 2018.