Fair Value of Financial Instruments - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Sep. 30, 2020		Dec. 31, 2019
Financial assets:
Securities held-to-maturity		$ 1,060,847		$ 201,217
Off-balance sheet instruments:
Commitments to extend credit	[1]	21,200		2,400
Standby letters of credit		1,600	[1]	1,400
Quoted market prices in an active market (Level 1)
Financial assets:
Securities held-to-maturity		0		0
Loans, net		0		0
Consumer loans held-for-sale		0		0
Commercial loans held-for-sale		0		0
Financial liabilities:
Deposits and securities sold under agreements to repurchase		0		0
Federal Home Loan Bank advances		0		0
Subordinated debt and other borrowings		0		0
Off-balance sheet instruments:
Commitments to extend credit	[1]	0		0
Models with significant observable market parameters (Level 2)
Financial assets:
Securities held-to-maturity		1,060,847		201,217
Loans, net		0		0
Consumer loans held-for-sale		84,877		82,986
Commercial loans held-for-sale		12,606		17,836
Financial liabilities:
Deposits and securities sold under agreements to repurchase		0		0
Federal Home Loan Bank advances		0		0
Subordinated debt and other borrowings		0		0
Off-balance sheet instruments:
Commitments to extend credit	[1]	0		0
Models with significant unobservable market parameters (Level 3)
Financial assets:
Securities held-to-maturity		0		0
Loans, net		22,483,708		19,717,845
Consumer loans held-for-sale		0		0
Commercial loans held-for-sale		0		0
Financial liabilities:
Deposits and securities sold under agreements to repurchase		25,804,207		19,647,392
Federal Home Loan Bank advances		1,428,059		2,078,514
Subordinated debt and other borrowings		681,964		712,220
Off-balance sheet instruments:
Commitments to extend credit	[1]	22,784		3,786
Carrying/ Notional Amount
Financial assets:
Securities held-to-maturity		1,039,650		188,996
Loans, net		22,188,764		19,693,099
Consumer loans held-for-sale		82,748		81,820
Commercial loans held-for-sale		12,290		17,585
Financial liabilities:
Deposits and securities sold under agreements to repurchase		26,671,015		20,307,382
Federal Home Loan Bank advances		1,287,738		2,062,534
Subordinated debt and other borrowings		670,273		749,080
Off-balance sheet instruments:
Commitments to extend credit	[1]	9,374,780		8,141,920
Estimated Fair Value
Financial assets:
Securities held-to-maturity	[2]	1,060,847		201,217
Loans, net	[2]	22,483,708		19,717,845
Consumer loans held-for-sale	[2]	84,877		82,986
Commercial loans held-for-sale	[2]	12,606		17,836
Financial liabilities:
Deposits and securities sold under agreements to repurchase	[2]	25,804,207		19,647,392
Federal Home Loan Bank advances	[2]	1,428,059		2,078,514
Subordinated debt and other borrowings	[2]	681,964		712,220
Off-balance sheet instruments:
Commitments to extend credit	[1],[2]	$ 22,784		$ 3,786

[1] At the end of each quarter, Pinnacle Financial evaluates the inherent risks of the outstanding off-balance sheet commitments, including both commitments for unfunded loans and standby letters of credit. In making this evaluation, Pinnacle Financial utilizes credit loss expectations on funded loans from our allowance for credit losses methodology and evaluates the probability that the outstanding commitment will eventually become a funded loan. As a result, at September 30, 2020 and December 31, 2019, Pinnacle Financial included in other liabilities $21.2 million and $2.4 million, respectively, representing expected credit losses on off-balance sheet commitments, which are reflected in the estimated fair values of the related commitments. Also included in the fair values at September 30, 2020 and December 31, 2019 are unamortized fees related to these commitments of $1.6 million and $1.4 million, respectively.

[2] Estimated fair values are consistent with an exit-price concept. The assumptions used to estimate the fair values are intended to approximate those that a market-participant would realize in a hypothetical orderly transaction.