Loans and Allowance for Loan Losses - Loan Classification by Risk Rating Category (Details) - USD ($)		Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 17,464,009,000	$ 15,633,116,000
Potential problem loans not included in nonperforming assets		202,500,000	164,000,000
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		17,103,690,000	15,237,775,000
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		75,764,000	168,713,000
Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	206,687,000	169,173,000
Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		77,868,000	57,455,000
Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Commercial real estate - mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans		7,215,119,000	6,669,610,000
Commercial real estate - mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		7,058,133,000	6,487,368,000
Commercial real estate - mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		30,291,000	94,134,000
Commercial real estate - mortgage | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	96,729,000	72,044,000
Commercial real estate - mortgage | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		29,966,000	16,064,000
Commercial real estate - mortgage | Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Consumer real estate - mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans		2,815,160,000	2,561,214,000
Consumer real estate - mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		2,766,126,000	2,503,688,000
Consumer real estate - mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		10,534,000	18,356,000
Consumer real estate - mortgage | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	13,234,000	21,053,000
Consumer real estate - mortgage | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		25,266,000	18,117,000
Consumer real estate - mortgage | Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans		2,059,009,000	1,908,288,000
Construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		2,046,299,000	1,880,704,000
Construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		3,002,000	8,148,000
Construction and land development | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	6,313,000	13,468,000
Construction and land development | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		3,395,000	5,968,000
Construction and land development | Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans		5,006,247,000	4,141,341,000
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		4,866,409,000	4,014,656,000
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		31,213,000	46,898,000
Commercial and industrial | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	90,345,000	62,529,000
Commercial and industrial | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		18,280,000	17,258,000
Commercial and industrial | Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans		368,474,000	352,663,000
Consumer and other | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		366,723,000	351,359,000
Consumer and other | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		724,000	1,177,000
Consumer and other | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	66,000	79,000
Consumer and other | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		961,000	48,000
Consumer and other | Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 0	$ 0

[1] Potential problem loans represent those loans with a well-defined weakness and where information about possible credit problems of borrowers has caused management to have doubts about the borrower's ability to comply with present repayment terms. This definition is believed to be substantially consistent with the standards established by Pinnacle Bank's primary regulators for loans classified as substandard, excluding the impact of nonaccrual loans and troubled debt restructurings. Potential problem loans, which are not included in nonaccrual loans, amounted to approximately $202.5 million at September 30, 2018, compared to $164.0 million at December 31, 2017.