CONDENSED STATEMENT OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($)	Total	Common Stock	Preferred Stock	Treasury Stock	Additional Paid in Capital	Retained Earnings
Balance at beginning of period at Dec. 31, 2017		$ 534,000	$ 0	$ 0	$ 329,993,000	$ 82,496,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock purchase				(12,100,000)
Stock compensation					4,679,000
Dividends paid					(91,122,000)	(264,228,000)
Other					(5,388,000)	0
Net income	$ 270,006,000					270,006,000
Balance at end of period at Jun. 30, 2018	314,870,000	534,000	0	(12,100,000)	238,162,000	88,274,000
Balance at beginning of period at Mar. 31, 2018		534,000	0	0	325,871,000	258,505,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock purchase				(12,100,000)
Stock compensation					4,481,000
Dividends paid					(91,122,000)	(261,543,000)
Other					(1,068,000)	0
Net income	91,312,000					91,312,000
Balance at end of period at Jun. 30, 2018	314,870,000	534,000	0	(12,100,000)	238,162,000	88,274,000
Balance at beginning of period at Dec. 31, 2018	712,612,000	533,000	0	(38,030,000)	239,827,000	510,282,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock purchase				(1,970,000)
Stock compensation					2,435,000
Dividends paid					0	(235,210,000)
Other					(1,242,000)	105,000
Net income	235,928,000					235,928,000
Balance at end of period at Jun. 30, 2019	712,658,000	533,000	0	(40,000,000)	241,020,000	511,105,000
Balance at beginning of period at Mar. 31, 2019		533,000	0	(40,000,000)	240,408,000	618,123,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock purchase				0
Stock compensation					1,327,000
Dividends paid					0	(232,604,000)
Other					(715,000)	105,000
Net income	125,481,000					125,481,000
Balance at end of period at Jun. 30, 2019	$ 712,658,000	$ 533,000	$ 0	$ (40,000,000)	$ 241,020,000	$ 511,105,000