Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($)	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, shares at Dec. 31, 2019		18,352,779
Restricted stock awards, net of forfeitures, shares		(52)
Common stock repurchased, shares	(725,220)	(725,220)
Restricted stock units converted to common stock, shares		21,971
Balance, shares at Mar. 31, 2020		17,649,478
Balance at Dec. 31, 2019	$ 2,355,300,000	$ 200,000	$ 157,700,000	$ 2,196,600,000	$ 800,000
Net income (loss)	(83,800,000)	0	0	(83,800,000)	0
Other comprehensive loss	(100,000)	0	0	0	(100,000)
Stock-based compensation	1,800,000	0	1,800,000	0	0
Common stock repurchased, value	(307,100,000)	0	(2,000,000.0)	(305,100,000)	0
Balance at Mar. 31, 2020	$ 1,966,100,000	$ 200,000	157,500,000	1,807,700,000	700,000
Balance, shares at Dec. 31, 2020	17,092,432	17,092,432
Restricted stock awards, net of forfeitures, shares		(18)
Common stock repurchased, shares	(393,408)	(393,408)
Restricted stock units converted to common stock, shares		11,416
Balance, shares at Mar. 31, 2021	16,710,422	16,710,422
Balance at Dec. 31, 2020	$ 2,302,500,000	$ 200,000	161,900,000	2,138,800,000	1,600,000
Net income (loss)	202,100,000	0	0	202,100,000	0
Other comprehensive loss	(700,000)	0	0	0	(700,000)
Stock-based compensation	1,100,000	0	1,100,000	0	0
Common stock repurchased, value	(135,200,000)	0	(1,300,000)	(133,900,000)	0
Balance at Mar. 31, 2021	$ 2,369,800,000	$ 200,000	$ 161,700,000	$ 2,207,000,000.0	$ 900,000