Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal									$ 69,427	$ 82,556	$ 94,112
State									4,072	3,808	3,257
Total									73,499	86,364	97,369
Deferred:
Federal									10,796	(6,400)	31,276
State									0	0	0
Total									10,796	(6,400)	31,276
Total expense:
Federal									80,223	76,156	125,388
State									4,072	3,808	3,257
Total	$ 16,539	$ 23,958	$ 21,387	$ 22,411	$ 19,200	$ 22,998	$ 18,424	$ 19,342	$ 84,295	$ 79,964	$ 128,645