Consolidated Statements of Shareholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Cumulative Effect, Period Of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] Retained Earnings [Member]
Shareholders' equity, beginning balance at Dec. 31, 2019		$ 98,828	$ 1,700,674	$ (2,014)	$ 1,698,660
Proceeds from stock options exercised		0
Share-based compensation expense		35
Withholding tax on stock options exercised		0
Net income (loss)	$ (139,204)		(139,204)
Dividends paid to shareholders			(34,875)
Shareholders' equity, ending balance at Mar. 31, 2020	1,623,444	98,863	1,524,581
Shareholders' equity, beginning balance at Dec. 31, 2020	2,032,597	98,970	1,933,627	$ 0	$ 1,933,627
Proceeds from stock options exercised		215
Share-based compensation expense		35
Withholding tax on stock options exercised		(383)
Net income (loss)	106,995		106,995
Dividends paid to shareholders			(35,022)
Shareholders' equity, ending balance at Mar. 31, 2021	$ 2,104,437	$ 98,837	$ 2,005,600