CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Balance (in shares) at Dec. 31, 2019		476,882	(78,957)
Balance at beginning of period at Dec. 31, 2019	$ 2,151,487	$ 47,688	$ (1,823,201)	$ 1,782,427	$ 1,360	$ 2,143,213
Increase (Decrease) in Stockholders' Equity
Net income	53,910					53,910
Stock amortization and vesting (in shares)		651
Stock amortization and vesting	2,951	$ 65		2,886
Cash dividends	(39,817)					(39,817)
Other comprehensive loss	(136)				(136)
Balance (in shares) at Mar. 31, 2020		477,533	(78,957)
Balance at end of period at Mar. 31, 2020	2,168,395	$ 47,753	$ (1,823,201)	1,785,313	1,224	2,157,306
Balance (in shares) at Dec. 31, 2020		477,829	(78,957)
Balance at beginning of period at Dec. 31, 2020	2,215,707	$ 47,783	$ (1,823,201)	1,804,354	2,419	2,184,352
Increase (Decrease) in Stockholders' Equity
Net income	126,354					126,354
Stock amortization and vesting (in shares)		548
Stock amortization and vesting	3,933	$ 55		3,878
Cash dividends	(39,887)					(39,887)
Other comprehensive loss	(137)				(137)
Balance (in shares) at Mar. 31, 2021		478,377	(78,957)
Balance at end of period at Mar. 31, 2021	$ 2,305,970	$ 47,838	$ (1,823,201)	$ 1,808,232	$ 2,282	$ 2,270,819