Condensed Statements of Shareholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Restatement Adjustment [Member] Retained Earnings [Member]
Beginning balance at Dec. 31, 2017	$ 1,762,574	$ 7	$ 360,153	$ (65,854)	$ 1,469,732	$ (1,464)
Share-based compensation	3,075		3,075
Repurchase of common stock	(959)			(959)
Proceeds from options exercised	2		2
Changes in comprehensive income	35					35
Net income	(44,922)
Ending balance at Mar. 31, 2018	1,719,805	7	363,230	(66,813)	1,424,810	(1,429)
Beginning balance at Dec. 31, 2017	1,762,574	7	360,153	(65,854)	1,469,732	(1,464)
Changes in comprehensive income	242
Net income	63,812
Ending balance at Sep. 30, 2018	1,833,782	7	368,452	(66,999)	1,533,544	(1,222)
Beginning balance at Mar. 31, 2018	1,719,805	7	363,230	(66,813)	1,424,810	(1,429)
Share-based compensation	2,306		2,306
Repurchase of common stock	(27)			(27)
Proceeds from options exercised	0		0
Changes in comprehensive income	162					162
Net income	11,254
Ending balance at Jun. 30, 2018	1,733,500	7	365,536	(66,840)	1,436,064	(1,267)
Share-based compensation	2,912		2,912
Repurchase of common stock	(159)			(159)
Proceeds from options exercised	4		4
Changes in comprehensive income	45					45
Net income	97,480
Ending balance at Sep. 30, 2018	1,833,782	7	368,452	(66,999)	1,533,544	(1,222)
Beginning balance at Dec. 31, 2018	1,928,504	7	371,225	(67,016)	1,625,481	(1,193)
Share-based compensation	3,671		3,671
Repurchase of common stock	(5,223)			(5,223)
Proceeds from options exercised	0		0
Changes in comprehensive income	177					177
Net income	56,076
Ending balance at Mar. 31, 2019	1,977,656	7	374,896	(72,239)	1,676,008	(1,016)
Ending balance (Accounting Standards Update 2016-02) at Mar. 31, 2019							$ (5,549)
Beginning balance at Dec. 31, 2018	1,928,504	7	371,225	(67,016)	1,625,481	(1,193)
Changes in comprehensive income	318
Net income	254,041
Ending balance at Sep. 30, 2019	2,180,087	7	379,354	(72,372)	1,873,973	(875)
Beginning balance at Mar. 31, 2019	1,977,656	7	374,896	(72,239)	1,676,008	(1,016)
Share-based compensation	2,742		2,742
Repurchase of common stock	(25)			(25)
Proceeds from options exercised	1		1
Changes in comprehensive income	152					152
Net income	114,501
Ending balance at Jun. 30, 2019	2,095,027	7	377,639	(72,264)	1,790,509	(864)
Share-based compensation	1,715		1,715
Repurchase of common stock	(108)			(108)
Proceeds from options exercised	0		0
Changes in comprehensive income	(11)					(11)
Net income	83,464
Ending balance at Sep. 30, 2019	$ 2,180,087	$ 7	$ 379,354	$ (72,372)	$ 1,873,973	$ (875)