Summary of Income Tax Expense (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current
Federal										$ 28,705,000	$ 21,860,000	$ 18,377,000
State										9,374,000	8,118,000	7,007,000
Total current income tax expense										38,079,000	29,978,000	25,384,000
Deferred
Federal	[1]									(3,451,000)	5,016,000	3,918,000
State	[1]									(629,000)	915,000	715,000
Total deferred income tax (benefit) expense	[1]									(4,080,000)	5,931,000	4,633,000
Total income tax expense		$ 8,341,000	$ 9,305,000	$ 7,488,000	$ 8,865,000	$ 8,846,000	$ 9,800,000	$ 8,350,000	$ 8,913,000	33,999,000	35,909,000	30,017,000
Tax benefit of operating loss carryforwards										$ 391,000	$ 0	$ 0

[1] Includes tax benefit of operating loss carryforwards of $391,000, $0 and $0 for the years ended December 31, 2015, 2014, and 2013, respectively.