Summary of Significant Accounting Policies - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share, Basic [Abstract]
Net income attributable to common stockholders	$ 107,583	$ 89,176	$ 93,650
Weighted-Average Shares (in shares)	10,758,000	10,728,000	10,696,000
Dollars per share (in dollars per share)	$ 10.00	$ 8.31	$ 8.76
Effect of dilutive securities
SARs and restricted stock (in shares)	88,000	58,000	82,000
SARs and restricted stock (in dollars per share)	$ (0.08)	$ (0.04)	$ (0.07)
Net income, Diluted EPS	$ 107,583	$ 89,176	$ 93,650
Weighted-Average Shares, Diluted EPS (in shares)	10,846,000	10,786,000	10,778,000
Diluted EPS (in dollars per share)	$ 9.92	$ 8.27	$ 8.69
Stock Appreciation Rights and Restricted Stock
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	39,326	74,336	43,374
Performance Shares
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	18,183	12,680	10,349