Regulatory Capital Requirements - Schedule of Capital Amounts and Ratios (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
CapStar Financial Holdings, Inc.
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital to risk-weighted assets, actual amount		$ 152,445	$ 149,616
Tier I capital to risk-weighted assets, actual amount		138,375	137,909
Tier I capital to average assets, actual amount		$ 138,375	$ 137,909
Total capital to risk-weighted assets, actual ratio		12.10%	12.60%
Tier I capital to risk-weighted assets, actual ratio		11.00%	11.60%
Tier I capital to average assets, actual ratio		10.40%	10.50%
Total capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 100,502	$ 95,028
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	75,377	71,271
Tier I capital to average assets, minimum capital requirement amount	[1]	$ 53,396	$ 52,727
Total capital to risk-weighted assets, minimum capital requirement ratio	[1]	8.00%	8.00%
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	6.00%	6.00%
Tier I capital to average assets, minimum capital requirement ratio	[1]	4.00%	4.00%
CapStar Financial Holdings, Inc. | Common Stock
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Tier I capital to risk-weighted assets, actual amount		$ 129,685	$ 129,528
Tier I capital to risk-weighted assets, actual ratio		10.30%	10.90%
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 56,533	$ 53,453
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	4.50%	4.50%
CapStar Bank
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital to risk-weighted assets, actual amount		$ 129,571	$ 126,718
Tier I capital to risk-weighted assets, actual amount		115,501	115,011
Tier I capital to average assets, actual amount		$ 115,501	$ 115,011
Total capital to risk-weighted assets, actual ratio		10.30%	10.70%
Tier I capital to risk-weighted assets, actual ratio		9.20%	9.70%
Tier I capital to average assets, actual ratio		8.70%	8.70%
Total capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 100,483	$ 95,028
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	75,362	71,271
Tier I capital to average assets, minimum capital requirement amount	[1]	$ 53,394	$ 52,727
Total capital to risk-weighted assets, minimum capital requirement ratio	[1]	8.00%	8.00%
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	6.00%	6.00%
Tier I capital to average assets, minimum capital requirement ratio	[1]	4.00%	4.00%
Total capital to risk-weighted assets, minimum to be well capitalized amount	[2]	$ 125,604	$ 118,785
Tier I capital to risk-weighted assets, minimum to be well capitalized amount	[2]	100,483	95,028
Tier I capital to average assets, minimum to be well capitalized amount	[2]	$ 66,742	$ 65,909
Total capital to risk-weighted assets, minimum to be well capitalized ratio	[2]	10.00%	10.00%
Tier I capital to risk-weighted assets, minimum to be well capitalized ratio	[2]	8.00%	8.00%
Tier I capital to average assets, minimum to be well capitalized ratio	[2]	5.00%	5.00%
CapStar Bank | Common Stock
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Tier I capital to risk-weighted assets, actual amount		$ 99,311	$ 99,130
Tier I capital to risk-weighted assets, actual ratio		7.90%	8.30%
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 56,522	$ 53,453
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	4.50%	4.50%
Tier I capital to risk-weighted assets, minimum to be well capitalized amount	[2]	$ 81,643	$ 77,210
Tier I capital to risk-weighted assets, minimum to be well capitalized ratio	[2]	6.50%	6.50%

[1] For the calendar year 2017, the Company must maintain a capital conservation buffer of Tier 1 common equity capital in excess of minimum risk-based capital ratios by at least 1.25% to avoid limits on capital distributions and certain discretionary bonus payments to executive officers and similar employees.

[2] For the Company to be well-capitalized, the Bank must be well-capitalized and the Company must not be subject to any written agreement, order, capital directive, or prompt corrective action directive issued by the Federal Reserve to meet and maintain a specific capital level for any capital measure.