Summary of Income Tax Expense (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current
Federal										$ 30,461,000	$ 28,705,000	$ 21,860,000
State										9,283,000	9,374,000	8,118,000
Total current income tax expense										39,744,000	38,079,000	29,978,000
Deferred
Federal	[1]									(70,000)	(3,451,000)	5,016,000
State	[1]									(12,000)	(629,000)	915,000
Total deferred income tax (benefit) expense	[1]									(82,000)	(4,080,000)	5,931,000
Total income tax expense		$ 9,662,000	$ 10,156,000	$ 10,492,000	$ 9,352,000	$ 8,341,000	$ 9,305,000	$ 7,488,000	$ 8,865,000	39,662,000	33,999,000	35,909,000
Tax benefit of operating loss carryforwards										$ 571,000	$ 391,000	$ 0

[1] Includes tax benefit of operating loss carryforwards of $571,000, $391,000 and $0 for the years ended December 31, 2016, 2015, and 2014, respectively.