Earnings per Share - Schedule of Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Numerator
Net income attributable to ACIC common stockholders	$ 19,397	$ 32,483	$ 60,547	$ 80,273
Denominator
Weighted-average shares outstanding	47,192,404	48,664,597	47,939,067	48,413,364
Effect of dilutive securities	1,217,484	1,253,132	1,201,752	1,300,171
Weighted-average diluted shares	48,409,888	49,917,729	49,140,819	49,713,535
Earnings available to ACIC common stockholders per share, Basic	$ 0.41	$ 0.67	$ 1.26	$ 1.66
Earnings available to ACIC common stockholders per share, Diluted	$ 0.4	$ 0.65	$ 1.23	$ 1.61