Significant Accounting Policies - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 08, 2020	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Accounting Policies [Abstract]
Accounting standards update				us-gaap:AccountingStandardsUpdate201613Member
Retained earnings		$ (192,072)	$ (192,072)	$ (152,819)
Unpaid obligations record as restricted assets		800	800	$ 300	$ 2
Minimum protective endowment held in an interest-bearing account		$ 500	$ 500		$ 500
Authorized shares of common stock		32,000,000	32,000,000	32,000,000
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01	$ 0.01
Issued shares of common stock		22,222,936	22,222,936	21,964,809
Outstanding shares of common stock		22,222,936	22,222,936	21,964,809
Authorized shares of preferred stock		8,000,000	8,000,000	8,000,000
Issued shares of preferred stock		0	0	0
Outstanding shares of preferred stock		0	0	0
Common stock dividends (in dollars per share)	$ 0.60
Accumulated other comprehensive income net of tax		$ 659	$ 659	$ 233
Tax from unrealized gains and losses on marketable securities			252	90
Reclassifications from AOCI		25	25
Reclassifications from AOCI, tax		10	10
Other Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Tuition receivable, noncurrent		$ 3,100	$ 3,100	1,000
Cumulative Effect Period of Adoption Adjustment
Accounting Policies [Abstract]
Retained earnings				$ 3,310