Schedule of Investments in and Advances to Affiliates (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2013
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	$ 8,615	[1]
Fair Value at the beginning of the period	492,797
Gross Additions	112,616	[2]
Gross Reductions	103,229	[3]
Fair Value at the end of the period	502,184
Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	7,429	[1]
Fair Value at the beginning of the period	283,575
Gross Additions	88,837	[2]
Gross Reductions	27,622	[3]
Fair Value at the end of the period	344,790
Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	1,186	[1]
Fair Value at the beginning of the period	209,222
Gross Additions	23,779	[2]
Gross Reductions	75,607	[3]
Fair Value at the end of the period	157,394
RECTORSEAL CORPORATION [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	5,915	[1]
Fair Value at the beginning of the period	166,300
Gross Additions	72,600	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	238,900
RECTORSEAL CORPORATION [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	27,907	[4]
WHITMORE MANUFACTURING COMPANY [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	1,509	[1]
Fair Value at the beginning of the period	67,200
Gross Additions	13,300	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	80,500
WHITMORE MANUFACTURING COMPANY [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	80	[4]
HEELYS, INC. [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	20,498
Gross Additions	0	[2]
Gross Reductions	20,498	[3]
Fair Value at the end of the period	0
HEELYS, INC. [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	9,317,310	[4]
MEDIA RECOVERY, INC. [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	15,600
Gross Additions	0	[2]
Gross Reductions	5,700	[3]
Fair Value at the end of the period	9,900
Shares in investment (in shares)	4,000,002	[4]
MEDIA RECOVERY, INC. [Member] | Control Investments [Member] | Series A Convertible Preferred Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	3,100
Gross Additions	0	[2]
Gross Reductions	1,100	[3]
Fair Value at the end of the period	2,000
Shares issued upon conversion (in shares)	800,000	[4]
BALCO, INC. [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	4,100
Gross Additions	400	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	4,500
BALCO, INC. [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	445,000	[4]
BALCO, INC. [Member] | Control Investments [Member] | Class B non voting common [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	60,920	[4]
CapStar Holdings Corporation [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	0
Gross Additions	1,668	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	1,668
Shares in investment (in shares)	1,000,000	[4]
CapStar Holdings Corporation [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Fair Value at the beginning of the period	5,338
Gross Additions	840	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	6,178
Shares in investment (in shares)	500	[4]
Discovery Alliance, LLC [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	1,280
Gross Additions	0	[2]
Gross Reductions	324	[3]
Fair Value at the end of the period	956
Ownership percentage (in hundredths)	90.00%	[4]
Humac Company [Member] | Control Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	5	[1]
Fair Value at the beginning of the period	159
Gross Additions	29	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	188
Humac Company [Member] | Control Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	1,041,000	[4]
ALAMO GROUP INC. [Member] | Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	764	[1]
Fair Value at the beginning of the period	85,139
Gross Additions	23,139	[2]
Fair Value at the end of the period	108,278
ALAMO GROUP INC. [Member] | Affiliated Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	2,830,300	[4]
ENCORE WIRE CORPORATION [Member] | Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	172	[1]
Fair Value at the beginning of the period	121,458
Gross Additions	0	[2]
Gross Reductions	75,507	[3]
Fair Value at the end of the period	45,951
ENCORE WIRE CORPORATION [Member] | Affiliated Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	1,312,500	[4]
PALLETONE, INC. [Member] | Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	250	[1]
Fair Value at the beginning of the period	2,000
Gross Additions	0	[2]
Gross Reductions	100	[3]
Fair Value at the end of the period	1,900
PALLETONE, INC. [Member] | Affiliated Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares in investment (in shares)	150,000	[4]
PALLETONE, INC. [Member] | Affiliated Investments [Member] | Senior Subordinated Notes [Member]
Investments in and Advances to Affiliates [Line Items]
Interest rate on notes (in hundredths)	12.30%	[4]
Amount of debt investment	2,000,000	[4]
BOXX TECHNOLOGIES, INC. [Member] | Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	600
Gross Additions	640	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	1,240
BOXX TECHNOLOGIES, INC. [Member] | Affiliated Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Conversion price per share (in dollars per share)	$ 0.50	[4]
BOXX TECHNOLOGIES, INC. [Member] | Affiliated Investments [Member] | Series B Convertible Preferred Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares issued upon conversion (in shares)	3,125,354	[4]
WELLOGIX, INC. [Member] | Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Amount of Interest, Fees or Dividends Credited in Income	0	[1]
Fair Value at the beginning of the period	25
Gross Additions	0	[2]
Gross Reductions	0	[3]
Fair Value at the end of the period	$ 25
WELLOGIX, INC. [Member] | Affiliated Investments [Member] | Common Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Conversion price per share (in dollars per share)	$ 1.0441	[4]
WELLOGIX, INC. [Member] | Affiliated Investments [Member] | Series A-1 Preferred Stock [Member]
Investments in and Advances to Affiliates [Line Items]
Shares issued upon conversion (in shares)	4,788,371	[4]

[1] Represents the total amount of interest, fees and dividends, credited to income for the portion of the year an investment was included in the Control or Non-Control/Non-Affiliate categories, respectively.

[2] Gross additions include increases in the cost basis of investments resulting from new portfolio investments, follow-on investments and accrued PIK interest, and the exchange of one or more existing securities for one or more new securities. Gross additions also include net increases in unrealized appreciation or net decreases in unrealized depreciation as well as movement of an existing portfolio company into this category and out of a different category.

[3] Gross reductions included in decreases in the cost basis of investment resulting from principal payments or sales and exchanges of one or more existing securities for one or more new securities. Gross reductions also include net increases in unrealized depreciation or net decreases in unrealized appreciation as well as the movement of an existing portfolio company out of this category and into a different category.

[4] The principal amount and ownership detail as shown in the Consolidated Schedules of Investments.