SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Basic EPS
Net income attributable to common stockholders	$ 40,313	$ 40,421	$ 87,268	$ 80,665
Net income attributable to common stockholders (in shares)	10,879,000	10,833,000	10,863,000	10,817,000
Net income attributable to common stockholders (in dollars per share)	$ 3.71	$ 3.73	$ 8.04	$ 7.46
Effect of dilutive securities
SARs and restricted stock units (in shares)	77,000	83,000	103,000	100,000
SARs and restricted stock units (in dollars per share)	$ (0.03)	$ (0.03)	$ (0.08)	$ (0.07)
Net income, diluted EPS	$ 40,313	$ 40,421	$ 87,268	$ 80,665
Weighted-Average Shares, diluted EPS (in shares)	10,956,000	10,916,000	10,966,000	10,917,000
Diluted EPS (in dollars per share)	$ 3.68	$ 3.70	$ 7.96	$ 7.39
Stock Appreciation Rights and Restricted Stock
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	43,263	34,500	46,317	48,605
Performance Shares
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	29,918	32,282	29,918	32,282