SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Basic EPS
Net income attributable to common stockholders	$ 49,170	$ 40,313	$ 93,155	$ 87,268
Net income attributable to common stockholders (in shares)	10,933,000	10,879,000	10,915,000	10,863,000
Net income attributable to common stockholders (in dollars per share)	$ 4.50	$ 3.71	$ 8.53	$ 8.04
Effect of dilutive securities
SARs and restricted stock units (in shares)	30,000	77,000	58,000	103,000
SARs and restricted stock units (in dollars per share)	$ (0.02)	$ (0.03)	$ (0.04)	$ (0.08)
Net income, diluted EPS	$ 49,170	$ 40,313	$ 93,155	$ 87,268
Weighted-average shares, diluted EPS (in shares)	10,963,000	10,956,000	10,973,000	10,966,000
Diluted EPS (in dollars per share)	$ 4.48	$ 3.68	$ 8.49	$ 7.96
Stock Appreciation Rights and Restricted Stock
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	76,166	43,263	67,353	46,317
Performance Shares
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	29,507	29,918	29,507	29,918