Changes in Accumulated Other Comprehensive Income by Component - Summary of Changes (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 338,842	$ 296,456	$ 275,830
Other comprehensive income (loss) before reclassifications	1,149	(1,005)	535
Losses (gains) reclassified from other comprehensive income	7	143	(17)
Net current period other comprehensive income (loss)	1,156	(862)	518
Balance	399,952	338,842	296,456
Realized (loss) gain on sales of available-for-sale securities		200
Changes in other comprehensive income (loss), tax expense (benefit)	300	(500)	300
Accumulated Other Comprehensive Income (Loss), net of Taxes
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(319)	543	25
Balance	837	$ (319)	543
Maximum
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Realized (loss) gain on sales of available-for-sale securities	$ (100)		$ 100

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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