Stockholders' Equity - Accumulated other comprehensive income (loss) activity (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	$ 766,703	$ 856,656	$ 808,897	$ 883,450
Balance at the end of the period	747,511	839,530	747,511	839,530
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	4,487	3,081	3,234	331
Other comprehensive income (loss) before reclassification	(371)	379	1,344	3,413
Amount reclassified from accumulated other comprehensive income	(191)	(177)	(653)	(461)
Net current period other comprehensive income (loss)	(562)	202	691	2,952
Balance at the end of the period	3,925	3,283	3,925	3,283
Unrealized gains (losses) on AFS investment securities
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	3,874	2,142	2,521	(797)
Other comprehensive income (loss) before reclassification	(371)	379	1,344	3,413
Amount reclassified from accumulated other comprehensive income	(140)	(83)	(502)	(178)
Net current period other comprehensive income (loss)	(511)	296	842	3,235
Balance at the end of the period	3,363	2,438	3,363	2,438
Postretirement benefits unrealized gains (losses)
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	613	939	713	1,128
Amount reclassified from accumulated other comprehensive income	(51)	(94)	(151)	(283)
Net current period other comprehensive income (loss)	(51)	(94)	(151)	(283)
Balance at the end of the period	$ 562	$ 845	$ 562	$ 845

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

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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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Amount after tax and reclassifications from recently adopted ASUS of other comprehensive income (loss) attributable to parent entity.

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