Quarterly Results (Unaudited) - Summary of Unaudited Quarterly Results of Operations (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 145,510,000	$ 141,506,000	$ 136,028,000	$ 129,600,000	$ 147,024,000	$ 148,092,000	$ 146,970,000	$ 150,139,000	$ 552,644,000	$ 592,225,000	$ 595,740,000
Gross Profit	35,719,000	30,893,000	30,503,000	26,509,000	30,691,000	29,253,000	32,843,000	33,134,000	123,624,000	125,921,000	124,809,000
Net income	$ 14,809,000	$ 11,380,000	$ 11,865,000	$ 8,302,000	$ 11,747,000	$ 9,352,000	$ 12,871,000	$ 13,407,000	$ 46,356,000	$ 47,377,000	$ 46,703,000
Net Income per Basic Common Share	$ 0.83	$ 0.64	$ 0.66	$ 0.46	$ 0.65	$ 0.51	$ 0.70	$ 0.72	$ 2.59	$ 2.59	$ 2.48
Net Income per Diluted Common Share	$ 0.81	$ 0.63	$ 0.65	$ 0.46	$ 0.64	$ 0.50	$ 0.69	$ 0.71	$ 2.55	$ 2.55	$ 2.46