Acquisition - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Apr. 03, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Common stock outstanding	9,213,036us-gaap_CommonStockSharesOutstanding		8,630,966us-gaap_CommonStockSharesOutstanding
Net intangible assets acquired		$ 822,000
Acquisition of goodwill	28,176,000us-gaap_Goodwill	8,428,000us-gaap_Goodwill	19,748,000us-gaap_Goodwill
Purchase price of the business assets		2,548,000
Summit [Member]
Business Acquisition [Line Items]
Date of acquisition agreement	Apr. 03, 2014
Exchange ratio per share to Heartland shareholder		49.04%
Share of common stock outstanding per share		$ 5.15
Common stock outstanding		1,164,442
Common stock issued	570,820
Market closing price per share		$ 22.23
Transaction value is estimated		18,900,000
Costs related to the acquisition	1,300,000
Net tangible assets acquired		19,900,000
Net intangible assets acquired		822,000
Acquisition of goodwill		8,400,000
Purchase price of the business assets		4,400,000
Core deposit intangible amortization period	7 years
Loan portfolio acquired		130,500,000
Discount on loan portfolio acquired		6,400,000
Performing portion of the loan portfolio acquired		106,200,000
Estimated fair value of performing portion of the loan portfolio		$ 104,600,000

Loan portfolio acquired.

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Business Combination Merger Consideration Price Per Share

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Business combination recognized identifiable assets acquired and liabilities assumed tangible assets.

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Discount on loan portfolio acquired.

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Estimated fair value of performing portion of the loan portfolio.

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Exchange ratio per share.

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Performing portion of the loan portfolio acquired.

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- Definition

Date when the business acquisition agreement was executed, in CCYY-MM-DD format.

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- Definition

Number of shares of equity interests issued or issuable to acquire entity.

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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

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- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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