SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Basic EPS
Net income attributable to common stockholders	$ 48,700	$ 42,312	$ 141,855	$ 129,580
Net income attributable to common stockholders (in shares)	10,934,000	10,883,000	10,921,000	10,869,000
Net income attributable to common stockholders (in dollars per share)	$ 4.45	$ 3.89	$ 12.99	$ 11.93
Effect of dilutive securities
SARs and restricted stock units (in shares)	38,000	83,000	52,000	99,000
SARs and restricted stock units (in dollars per share)	$ (0.01)	$ (0.03)	$ (0.06)	$ (0.11)
Net income, diluted EPS	$ 48,700	$ 42,312	$ 141,855	$ 129,580
Weighted-average shares, diluted EPS (in shares)	10,972,000	10,966,000	10,973,000	10,968,000
Diluted EPS (in dollars per share)	$ 4.44	$ 3.86	$ 12.93	$ 11.82
Stock Appreciation Rights and Restricted Stock
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	27,160	15,465	53,955	36,033
Performance Shares
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	27,580	29,918	28,865	29,918