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, 2018		18,972,558
Restricted stock awards, net of forfeitures, shares		5,282
Common stock repurchased, shares	(268,611)	(268,611)
Restricted stock units converted to common stock, shares		87,842
Balance, shares at Mar. 31, 2019		18,797,071
Balance at Dec. 31, 2018	$ 1,990,900,000	$ 200,000	$ 154,900,000	$ 1,836,100,000	$ (300,000)
Net income (loss)	164,400,000	0	0	164,400,000	0
Other comprehensive income (loss)	600,000	0	0	0	600,000
Stock-based compensation	2,200,000	0	2,200,000	0	0
Common stock repurchased, value	(109,200,000)	0	(4,900,000)	(104,300,000)	0
Balance at Mar. 31, 2019	$ 2,048,900,000	$ 200,000	152,200,000	1,896,200,000	300,000
Balance, shares at Dec. 31, 2019	18,972,558	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	17,649,748	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 income (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