Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income
Beginning balance (in shares) at Dec. 31, 2017			11,167,425
Beginning balance at Dec. 31, 2017	$ 209,197	$ (171)	$ 112	$ 47,079	$ 162,006	$ (171)	$ 0
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Issuance of stock in connection with the acquisition of Capella Education Company (in shares)			10,263,775
Issuance of stock in connection with the acquisition of Capella Education Company	1,236,961		$ 103	1,236,858
Filing fee related to new stock issuance	(148)			(148)
Stock-based compensation	14,994			14,994
Exercise of stock options, net (in shares)			156,424
Exercise of stock options, net	8,648		$ 1	8,647
Issuance of restricted stock, net (in shares)			155,874
Issuance of restricted stock, net	(776)		$ 1	(777)
Common stock dividends	(27,842)				(27,842)
Foreign currency translation adjustments	0
Unrealized gains on marketable securities, net of tax	32						32
Net income (loss)	(15,671)				(15,671)
Ending balance (in shares) at Dec. 31, 2018			21,743,498
Ending balance at Dec. 31, 2018	1,425,224		$ 217	1,306,653	118,322		32
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Stock-based compensation	12,116			12,033	83
Exercise of stock options, net (in shares)			103,364
Exercise of stock options, net	(1,773)		$ 2	(1,775)
Issuance of restricted stock, net (in shares)			117,947
Issuance of restricted stock, net	(7,472)		$ 1	(7,473)
Common stock dividends	(46,724)				(46,724)
Foreign currency translation adjustments	0
Unrealized gains on marketable securities, net of tax	201						201
Net income (loss)	81,138				81,138
Ending balance (in shares) at Dec. 31, 2019			21,964,809
Ending balance at Dec. 31, 2019	$ 1,462,710	$ (3,311)	$ 220	1,309,438	152,819	$ (3,311)	233
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Accounting standards update	us-gaap:AccountingStandardsUpdate201613Member
Issuance of common stock in public offering (in shares)			2,185,000
Issuance of common stock in public offering	$ 220,248		$ 22	220,226
Stock-based compensation	14,610			14,593	17
Exercise of stock options, net (in shares)			20,522
Exercise of stock options, net	1,244			1,244
Issuance of restricted stock, net (in shares)			250,377
Issuance of restricted stock, net	(25,845)		$ 2	(25,847)
Repurchase of common stock (in shares)			(1,769)
Repurchase of common stock	(247)			(105)	(142)
Common stock dividends	(56,005)				(56,005)
Foreign currency translation adjustments	48,068						48,068
Unrealized gains on marketable securities, net of tax	579						579
Net income (loss)	86,268				86,268
Ending balance (in shares) at Dec. 31, 2020			24,418,939
Ending balance at Dec. 31, 2020	$ 1,748,319		$ 244	$ 1,519,549	$ 179,646		$ 48,880