Summary of Significant Accounting Policies - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic EPS
Net income attributable to common stockholders	$ 9,399	$ 21,874
Weighted-Average Shares (in shares)	10,712,000	10,670,000
Dollars per share (in dollars per share)	$ 0.88	$ 2.05
Effect of dilutive securities
SARs and restricted stock (in shares)	70,000	107,000
SARs and restricted stock (in dollars per share)	$ (0.01)	$ (0.02)
Net income, Diluted EPS	$ 9,399	$ 21,874
Weighted-Average Shares, Diluted EPS (in shares)	10,782,000	10,777,000
Diluted EPS (in dollars per share)	$ 0.87	$ 2.03
Stock Appreciation Rights and Restricted Stock
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	87,148	56,976
Performance Shares
Effect of dilutive securities
Antidilutive securities excluded from earnings per share (in shares)	12,680	12,284