Summary of Income Tax Expense (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current
Federal										$ 21,510,000	$ 29,555,000	$ 30,461,000
State										11,960,000	9,183,000	9,283,000
Total current income tax expense										33,470,000	38,738,000	39,744,000
Deferred
Federal	[1]									5,372,000	22,246,000	(70,000)
State	[1]									1,489,000	3,641,000	(12,000)
Total deferred income tax expense (benefit)	[1]									6,861,000	25,887,000	(82,000)
Total income tax expense		$ 11,647,000	$ 10,802,000	$ 9,485,000	$ 8,397,000	$ 31,327,000	$ 11,639,000	$ 11,905,000	$ 9,754,000	40,331,000	64,625,000	39,662,000
Tax benefit of operating loss carryforwards										$ 443,000	$ 644,000	$ 571,000

[1] Includes tax benefit of operating loss carryforwards of $443,000, $644,000 and $571,000 for the years ended December 31, 2018, 2017, and 2016, respectively.