Loans and Allowance for Loan Losses - Financing Receivables Past Due (Details) - USD ($)		Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		$ 14,758,764,516	$ 8,449,924,736
Purchased credit impaired	[1]	48,501,000	31,612,000
Nonaccrual		19,204,000	18,742,000
Currently performing impaired loans		10,000,000	16,700,000
Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		34,874,000	0
Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		21,012,000	8,836,000
Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		28,894,000	22,330,000
30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		27,203,000	21,196,000
90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		1,691,000	1,134,000
Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		14,654,781,000	8,400,018,000
Commercial real estate - mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		6,387,372,000	3,193,496,000
Commercial real estate - mortgage | Owner-occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		2,368,641,000	1,354,893,000
Nonaccrual		2,249,000	2,297,000
Commercial real estate - mortgage | Owner-occupied | Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		6,545,000	0
Commercial real estate - mortgage | Owner-occupied | Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		3,296,000	1,956,000
Commercial real estate - mortgage | Owner-occupied | Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		3,872,000	3,505,000
Commercial real estate - mortgage | Owner-occupied | 30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		3,872,000	3,505,000
Commercial real estate - mortgage | Owner-occupied | 90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		0	0
Commercial real estate - mortgage | Owner-occupied | Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		2,352,679,000	1,347,134,000
Commercial real estate - mortgage | All other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		4,018,731,000	1,838,603,000
Nonaccrual		819,000	240,000
Commercial real estate - mortgage | All other | Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		11,061,000	0
Commercial real estate - mortgage | All other | Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		3,752,000	428,000
Commercial real estate - mortgage | All other | Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		1,820,000	0
Commercial real estate - mortgage | All other | 30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		1,820,000	0
Commercial real estate - mortgage | All other | 90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		0	0
Commercial real estate - mortgage | All other | Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		4,001,279,000	1,837,936,000
Consumer real estate - mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		2,552,927,000	1,185,917,000
Nonaccrual		8,133,000	5,554,000
Consumer real estate - mortgage | Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		9,081,000	0
Consumer real estate - mortgage | Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		10,431,000	2,520,000
Consumer real estate - mortgage | Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		7,689,000	3,891,000
Consumer real estate - mortgage | 30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		7,689,000	3,838,000
Consumer real estate - mortgage | 90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		0	53,000
Consumer real estate - mortgage | Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		2,517,593,000	1,173,953,000
Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		1,772,799,000	912,673,000
Nonaccrual		1,121,000	3,205,000
Construction and land development | Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		7,628,000	0
Construction and land development | Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		2,751,000	3,408,000
Construction and land development | Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		6,250,000	2,210,000
Construction and land development | 30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		6,250,000	2,210,000
Construction and land development | 90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		0	0
Construction and land development | Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		1,755,049,000	903,850,000
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		3,688,357,000	2,891,710,000
Nonaccrual		6,429,000	6,971,000
Commercial and industrial | Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		559,000	0
Commercial and industrial | Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		779,000	524,000
Commercial and industrial | Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		3,952,000	4,475,000
Commercial and industrial | 30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		2,880,000	4,475,000
Commercial and industrial | 90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		1,072,000	0
Commercial and industrial | Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		3,676,638,000	2,879,740,000
Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		357,310,000	266,129,000
Nonaccrual		453,000	475,000
Consumer and other | Purchased credit impaired, accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		0	0
Consumer and other | Purchased credit impaired, nonaccruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired		3,000	0
Consumer and other | Past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		5,311,000	8,249,000
Consumer and other | 30-89 days past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		4,692,000	7,168,000
Consumer and other | 90 days or more past due and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		619,000	1,081,000
Consumer and other | Current and accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		$ 351,543,000	$ 257,405,000

[1] Unpaid principal balance presented net of fair value adjustments recorded in conjunction with purchase accounting.