Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Net income	$ 1,952	$ 63,722	$ 12,631	$ 27,280	$ 20,534	$ 20,427	$ 65,674	$ 40,961
Less income allocated to non-controlling interests	(82)				(88)		(171)	(169)
Less income allocated to participating securities:
Non-forfeitable dividends on participating securities	(97)				(94)		(191)	(186)
Income allocated to participating securities							(87)
Total net income allocated to participating securities	(97)				(94)		(278)	(186)
Net income available to common stockholders	1,773				20,352		65,225	40,606
Net income for diluted net income per share	$ 1,773				$ 20,352		$ 65,225	$ 40,606
Reconciliation of shares
Shares for basic net income per share	39,055				39,577		39,298	39,555
Effect of dilutive securities: (Shares)
Total effect of dilutive securities (in shares)	82				192		82	192
Shares for diluted net income per share	39,137				39,769		39,380	39,747
Basic (in dollars per share)	$ 0.05				$ 0.51		$ 1.66	$ 1.03
Diluted (in dollars per share)	$ 0.05				$ 0.51		$ 1.66	$ 1.02
Stock options
Effect of dilutive securities: (Shares)
Stock options and performance-based stock units (in shares)					5			5
Performance-based stock units
Effect of dilutive securities: (Shares)
Stock options and performance-based stock units (in shares)	82				187		82	187