Changes in Shareholders' Equity and Comprehensive Income: (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance at March 31, 2016:			$ 83,195
Excess tax benefits related to restricted stock			(115)	$ (92)
Net income	$ 4,899	$ 4,502	11,493	$ 10,259
Ending balance at september 30, 2016:	87,964		87,964
Additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance at March 31, 2016:			4,871
Share based compensation			946
Dividends declared
Excess tax benefits related to restricted stock			115
Net income
Ending balance at september 30, 2016:	5,932		5,932
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance at March 31, 2016:			78,295
Share based compensation
Dividends declared			(7,786)
Excess tax benefits related to restricted stock
Net income			11,493
Ending balance at september 30, 2016:	$ 82,002		$ 82,002