Loans and Allowance for Loan Losses - Loan Classification by Risk Rating Category (Details) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 18,174,906,000	$ 17,707,549,000
Potential problem loans not included in nonperforming assets		190,300,000	176,300,000
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		17,776,254,000	17,346,673,000
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		109,001,000	93,163,000
Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	193,507,000	179,879,000
Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		96,144,000	87,834,000
Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Commercial real estate - mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans		7,419,146,000	7,164,954,000
Commercial real estate - mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		7,252,503,000	6,998,485,000
Commercial real estate - mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		51,552,000	55,932,000
Commercial real estate - mortgage | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	76,171,000	78,202,000
Commercial real estate - mortgage | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		38,920,000	32,335,000
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		2,887,628,000	2,844,447,000
Consumer real estate - mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		2,830,701,000	2,787,570,000
Consumer real estate - mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		6,916,000	7,902,000
Consumer real estate - mortgage | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	17,880,000	20,906,000
Consumer real estate - mortgage | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		32,131,000	28,069,000
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		2,097,570,000	2,072,455,000
Construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		2,083,602,000	2,059,376,000
Construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		7,843,000	4,334,000
Construction and land development | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	3,350,000	5,358,000
Construction and land development | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		2,775,000	3,387,000
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		5,419,520,000	5,271,421,000
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		5,259,503,000	5,148,726,000
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		41,980,000	24,284,000
Commercial and industrial | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	96,049,000	75,351,000
Commercial and industrial | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		21,988,000	23,060,000
Commercial and industrial | Doubtful-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0	0
Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans		351,042,000	354,272,000
Consumer and other | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		349,945,000	352,516,000
Consumer and other | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		710,000	711,000
Consumer and other | Substandard-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans	[1]	57,000	62,000
Consumer and other | Substandard-nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans		330,000	983,000
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 troubled debt restructurings. Potential problem loans, which are not included in nonaccrual loans, amounted to approximately $190.3 million at March 31, 2019, compared to $176.3 million at December 31, 2018.