Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income (Numerator)
Income available to common stockholders, Basic									$ 374,607	$ 320,087	$ (5,728)
Income available to common stockholders after assumed conversions, Diluted									$ 374,607	$ 320,087	$ (5,728)
Weighted Shares (Denominator)
Weighted shares, basic (in shares)									55,358,000	55,351,000	55,335,000
Weighted shares, diluted (in shares)									55,358,000	55,360,000	55,335,000
Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]
Basic (in dollars per share)	$ 3.01	$ 2.15	$ 4.12	$ (2.51)	$ 0.57	$ 1.25	$ 1.50	$ 2.46	$ 6.77	$ 5.78	$ (0.10)
Diluted (in dollars per share)	$ 3.01	$ 2.15	$ 4.12	$ (2.51)	$ 0.57	$ 1.25	$ 1.50	$ 2.45	$ 6.77	$ 5.78	$ (0.10)
Common Stock [Member]
Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]
Potentially dilutive securities (in shares)									67,500	0	78,500
Stock Options [Member]
Income (Numerator)
Effect of dilutive securities: Options									$ 0	$ 0	$ 0
Weighted Shares (Denominator)
Effect of dilutive securities: options (in shares)									0	9,000	0