Loans and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Allowance for loan losses
Beginning balance	$ 51,458	$ 40,001	$ 56,896	$ 37,826
Provision charged to expense	21,000	2,850	34,950	5,700
Charge-offs	(1,276)	(1)	(20,736)	(1,265)
Recoveries	3	2	75	591
Ending balance	71,185	42,852	71,185	42,852
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					$ 6,992	$ 22,298
Collectively evaluated for impairment					64,193	34,598
Allowance for loan losses	51,458	42,852	56,896	37,826	71,185	56,896
Allocated to loans:
Individually evaluated for impairment					45,502	93,500
Collectively evaluated for impairment					4,383,739	3,768,207
Total Loans Receivable					4,429,241	3,861,707
Commercial
Allowance for loan losses
Beginning balance	21,129	20,506	35,864	16,584
Provision charged to expense	5,499	2,468	8,771	7,631
Charge-offs	(87)	0	(18,165)	(1,254)
Recoveries	2	1	73	14
Ending balance	26,543	22,975	26,543	22,975
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					2,933	19,942
Collectively evaluated for impairment					23,610	15,922
Allowance for loan losses	26,543	22,975	35,864	22,975	26,543	35,864
Allocated to loans:
Individually evaluated for impairment					11,831	70,876
Collectively evaluated for impairment					1,273,088	1,285,941
Total Loans Receivable					1,284,919	1,356,817
Energy
Allowance for loan losses
Beginning balance	7,599	7,090	6,565	10,262
Provision charged to expense	10,773	210	13,085	(3,538)
Charge-offs	(1,000)	0	(2,278)	0
Recoveries	0	0	0	576
Ending balance	17,372	7,300	17,372	7,300
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					1,942	1,949
Collectively evaluated for impairment					15,430	4,616
Allowance for loan losses	17,372	7,300	6,565	10,262	17,372	6,565
Allocated to loans:
Individually evaluated for impairment					15,532	9,744
Collectively evaluated for impairment					374,814	398,829
Total Loans Receivable					390,346	408,573
Commercial real estate
Allowance for loan losses
Beginning balance	12,623	7,471	8,085	6,755
Provision charged to expense	4,276	62	8,814	778
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	16,899	7,533	16,899	7,533
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					1,704	210
Collectively evaluated for impairment					15,195	7,875
Allowance for loan losses	16,899	7,533	8,085	7,533	16,899	8,085
Allocated to loans:
Individually evaluated for impairment					10,909	10,492
Collectively evaluated for impairment					1,130,368	1,013,549
Total Loans Receivable					1,141,277	1,024,041
Construction and land development
Allowance for loan losses
Beginning balance	5,021	2,585	3,516	2,475
Provision charged to expense	(2)	17	1,503	127
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	5,019	2,602	5,019	2,602
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					5,019	3,516
Allowance for loan losses	5,019	2,602	3,516	2,475	5,019	3,516
Allocated to loans:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					661,691	628,418
Total Loans Receivable					661,691	628,418
Residential real estate
Allowance for loan losses
Beginning balance	4,687	2,047	2,546	1,464
Provision charged to expense	370	91	2,511	674
Charge-offs	(189)	0	(189)	0
Recoveries	0	0	0	0
Ending balance	4,868	2,138	4,868	2,138
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					413	197
Collectively evaluated for impairment					4,455	2,349
Allowance for loan losses	4,868	2,138	2,546	2,138	4,868	2,546
Allocated to loans:
Individually evaluated for impairment					6,981	2,388
Collectively evaluated for impairment					529,289	396,307
Total Loans Receivable					536,270	398,695
Paycheck Protection Program (“PPP”)
Allowance for loan losses
Beginning balance	0	0	0	0
Provision charged to expense	0	0	0	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	0	0	0	0
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					0	0
Allowance for loan losses	0	0	0	0	0	0
Allocated to loans:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					369,022	0
Total Loans Receivable					369,022	0
Consumer
Allowance for loan losses
Beginning balance	399	302	320	286
Provision charged to expense	84	2	266	28
Charge-offs	0	(1)	(104)	(11)
Recoveries	1	1	2	1
Ending balance	484	304	484	304
Period end allowance for loan losses allocated to:
Individually evaluated for impairment					0	0
Collectively evaluated for impairment					484	320
Allowance for loan losses	$ 484	$ 304	$ 320	$ 304	484	320
Allocated to loans:
Individually evaluated for impairment					249	0
Collectively evaluated for impairment					45,467	45,163
Total Loans Receivable					$ 45,716	$ 45,163