Loans and Allowance for Loan Losses - Details on Allowance for Loan Losses and Recorded Investment by Loan Classification and Impairment Evaluation Method (Details) - USD ($)	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	$ 60,477,000		$ 57,888,000
Individually evaluated for impairment	1,467,000		1,092,000
Total allowance for loan losses	61,944,000	$ 58,350,000	58,980,000	$ 61,412,000	$ 62,239,000	$ 65,432,000
Collectively evaluated for impairment	14,669,426,000		8,407,339,000
Individually evaluated for impairment	33,453,000		33,750,000
Loans	14,758,764,516		8,449,924,736
Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	0		0
Loans acquired with deteriorated credit quality	55,886,000		8,836,000
Commercial real estate - mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	15,963,000		13,595,000
Individually evaluated for impairment	39,000		60,000
Total allowance for loan losses	16,002,000	14,168,000	13,655,000	13,665,000	13,551,000	15,513,000
Collectively evaluated for impairment	6,359,443,000		3,188,362,000
Individually evaluated for impairment	3,275,000		2,750,000
Loans	6,387,372,000		3,193,496,000
Commercial real estate - mortgage | Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	0		0
Loans acquired with deteriorated credit quality	24,654,000		2,384,000
Consumer real estate - mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	6,891,000		5,874,000
Individually evaluated for impairment	944,000		690,000
Total allowance for loan losses	7,835,000	7,219,000	6,564,000	6,540,000	7,169,000	7,220,000
Collectively evaluated for impairment	2,522,372,000		1,174,456,000
Individually evaluated for impairment	11,043,000		8,941,000
Loans	2,552,927,000		1,185,917,000
Consumer real estate - mortgage | Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	0		0
Loans acquired with deteriorated credit quality	19,512,000		2,520,000
Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	5,104,000		3,604,000
Individually evaluated for impairment	22,000		20,000
Total allowance for loan losses	5,126,000	4,441,000	3,624,000	3,923,000	3,942,000	2,903,000
Collectively evaluated for impairment	1,761,298,000		906,053,000
Individually evaluated for impairment	1,122,000		3,212,000
Loans	1,772,799,000		912,673,000
Construction and land development | Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	0		0
Loans acquired with deteriorated credit quality	10,379,000		3,408,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	24,005,000		24,648,000
Individually evaluated for impairment	230,000		95,000
Total allowance for loan losses	24,235,000	22,912,000	24,743,000	25,090,000	24,144,000	23,643,000
Collectively evaluated for impairment	3,669,480,000		2,872,855,000
Individually evaluated for impairment	17,536,000		18,331,000
Loans	3,688,357,000		2,891,710,000
Commercial and industrial | Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	0		0
Loans acquired with deteriorated credit quality	1,341,000		524,000
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	7,317,000		9,293,000
Individually evaluated for impairment	232,000		227,000
Total allowance for loan losses	7,549,000	8,477,000	9,520,000	11,138,000	11,858,000	15,616,000
Collectively evaluated for impairment	356,833,000		265,613,000
Individually evaluated for impairment	477,000		516,000
Loans	357,310,000		266,129,000
Consumer and other | Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	0		0
Loans acquired with deteriorated credit quality	0		0
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	1,197,000		874,000
Individually evaluated for impairment	0		0
Total allowance for loan losses	1,197,000	$ 1,133,000	874,000	$ 1,056,000	$ 1,575,000	$ 537,000
Unallocated | Loans acquired with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total allowance for loan losses	$ 0		$ 0