Income Taxes (Tax Treatment of Distributions and Consolidated Benefit for Income Taxes) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax treatment of distributions:
Ordinary income (in dollars per share)									$ 0	$ 1.02814	$ 2.68216
Qualified ordinary income (in dollars per share)									0.00375	0.00337	0.05794
199A qualified business income									2.97465	0	0
Long-term capital gain (in dollars per share)									0.05916	1.07836	0.11613
Unrecaptured Section 1250 gain (in dollars per share)									0.12244	0.21513	0.10877
Distribution reported for 1099-DIV purposes (in dollars per share)									3.16000	2.32500	2.96500
Add: Dividend declared in current year and taxable in following year (in dollars per share)	$ 0.79250									0.79000	0
Less: Dividend declared in prior year and taxable in current year									(0.79000)	0	0
Dividends declared per common share (in dollars per share)		$ 0.79	$ 0.79	$ 0.79	$ 0.79	$ 0.775	$ 0.775	$ 0.775	$ 3.1625	$ 3.115	$ 2.965
Provision (benefit) for income taxes
Current - Federal									$ (2,953)	$ (5,672)	$ (2,991)
Current - State									1,332	1,119	1,241
Deferred - Federal									(32,492)	(54,396)	(19,539)
Deferred - State									(825)	3,237	(3,634)
Current - Foreign									1,892	2,307	1,067
Deferred - Foreign									(6,907)	(6,394)	(7,487)
Income tax benefit									$ (39,953)	$ (59,799)	$ (31,343)