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 (loss)	(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, 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 (loss)	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)