Significant Accounting Policies - Additional Information (Details) - USD ($)		3 Months Ended		12 Months Ended
	Mar. 16, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accounting Policies [Abstract]
Unpaid obligations record as restricted assets		$ 850,000	$ 5,000	$ 300,000
Minimum protective endowment held in an interest-bearing account		$ 500,000	$ 500,000
Authorized shares of common stock		32,000,000		32,000,000
Common stock, par value (in dollars per share)		$ 0.01		$ 0.01
Issued shares of common stock		22,213,587		21,964,809
Outstanding shares of common stock		22,213,587		21,964,809
Authorized shares of preferred stock		8,000,000		8,000,000
Issued shares of preferred stock		0		0
Outstanding shares of preferred stock		0		0
Common stock dividends (in dollar per share)	$ 0.60
Amount of antidilutive securities excluded from computation of earnings per share (in shares)		3,000	59,000
Accumulated other comprehensive income net of tax		$ 253,000		$ 233,000
Tax from unrealized gains and losses on marketable securities		98,000		90,000
Reclassifications from AOCI		0
Other Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Tuition receivable, noncurrent		$ 3,100,000		$ 1,000,000.0