Equity (Details) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
	Jan. 15, 2018	Sep. 22, 2017	Oct. 11, 2016	Sep. 27, 2012	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock Repurchase
Repurchase of common stock authorized by Board of Directors				$ 100,000
Number of years for repurchase of common stock				5 years
Common stock repurchased, value					$ 3,546	$ 28,958	$ 16,500
Shares issued					2,500	1,000
Temporary Equity, Par or Stated Value Per Share					$ 0.01	$ 0.01
Liquidation preference					20.00
Redemption price					$ 20.00
Common Stock
Common Stock Repurchase
Common stock repurchased (in shares)					155,000	1,212,000	912,000
Common stock repurchased, value					$ 2	$ 12	$ 9
Preferred Stock [Member]
Common Stock Repurchase
Shares issued					1,500,000	1,000,000
Redeemable Preferred Stock
Common Stock Repurchase
Shares issued			1,000,000
Dividend rate (as a percent)			6.50%
Temporary Equity, Par or Stated Value Per Share			$ 0.01
Purchase price			$ 20.00
Net proceeds after deducting investor fees					$ 19,800
Preferred stock dividends paid					1,300
Series A-2 Preferred Stock
Common Stock Repurchase
Shares issued		1,500,000
Dividend rate (as a percent)		6.50%
Temporary Equity, Par or Stated Value Per Share		$ 0.01
Purchase price		$ 20.00
Net proceeds after deducting investor fees					$ 29,700
Preferred stock dividends paid	$ 600
Dutch Auction [Member]
Common Stock Repurchase
Weighted average price per share (in dollars per share)					$ 22.83	$ 23.71