Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income	$ 12,338	$ 1,952	$ 63,722	$ 12,631	$ 27,280	$ 20,534	$ 20,427	$ 78,012	$ 68,241
Less income allocated to non-controlling interests	(121)				(88)			(292)	(257)
Less income allocated to participating securities:
Non-forfeitable dividends on participating securities	(103)				(93)			(294)	(279)
Income allocated to participating securities					(19)			(45)	(19)
Total net income allocated to participating securities	(103)				(112)			(339)	(298)
Net income available to common stockholders	12,114				27,080			77,381	67,686
Net income for diluted net income per share	$ 12,114				$ 27,080			$ 77,381	$ 67,686
Reconciliation of shares
Shares for basic net income per share	39,061				39,586			39,218	39,565
Effect of dilutive securities: (Shares)
Total effect of dilutive securities (in shares)	51				379			51	379
Shares for diluted net income per share	39,112				39,965			39,269	39,944
Basic (in dollars per share)	$ 0.31				$ 0.68			$ 1.97	$ 1.71
Diluted (in dollars per share)	$ 0.31				$ 0.68			$ 1.97	$ 1.69
Stock options
Effect of dilutive securities: (Shares)
Stock options and performance-based stock units (in shares)					4				4
Performance-based stock units
Effect of dilutive securities: (Shares)
Stock options and performance-based stock units (in shares)	51				375			51	375