Consolidated Statement Of Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Cumulative Dividends In Excess Of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Parent [Member]	Noncontrolling Interest [Member]
Balance, shares at Dec. 31, 2015		38,396,727
Balance, value at Dec. 31, 2015	$ 1,142,460,000	$ 384,000	$ 1,085,136,000	$ 19,862,000	$ 27,910,000	$ 1,133,292,000	$ 9,168,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to common stockholders	151,540,000			151,540,000	(22,179,000)	129,361,000	1,176,000
Comprehensive income	130,537,000
Distributions to noncontrolling interest	(1,565,000)						(1,565,000)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	(25,100,000)		(16,321,000)			(16,321,000)	(8,779,000)
Stock Issued During Period, Shares, New Issues		1,395,642
Stock Issued During Period, Value, New Issues	104,190,000	$ 14,000	104,176,000			104,190,000
Payments of Stock Issuance Costs	(1,133,000)		1,133,000			1,133,000
Shares issued on stock options exercised, shares		55,491
Shares issued on stock options exercised, value	(2,000)		(2,000)			(2,000)
Share-based Compensation			1,732,000
Share-based compensation	1,732,000					1,732,000
Dividends declared, $1.43 per share	(141,529,000)			(141,529,000)		(141,529,000)
Balance, shares at Dec. 31, 2016		39,847,860
Balance, value at Dec. 31, 2016	1,209,590,000	$ 398,000	1,173,588,000	29,873,000	5,731,000	1,209,590,000	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to common stockholders	159,365,000			159,365,000	(6,553,000)	152,812,000
Comprehensive income	152,812,000
Distributions to noncontrolling interest	(7,930,000)
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments			(7,930,000)			(7,930,000)
Stock Issued During Period, Shares, New Issues		1,661,161
Stock Issued During Period, Value, New Issues	122,237,000	$ 17,000	122,220,000			122,237,000
Adjustments Related to Tax Withholding for Share-based Compensation	(571,000)		(571,000)			(571,000)
Shares issued on stock options exercised, shares		23,133
Share-based Compensation			2,612,000
Share-based compensation	2,612,000					2,612,000
Dividends declared, $1.43 per share	$ (156,633,000)			(156,633,000)		(156,633,000)
Balance, shares at Dec. 31, 2017	41,532,154	41,532,154
Balance, value at Dec. 31, 2017	$ 1,322,117,000	$ 415,000	1,289,919,000	32,605,000	(822,000)	1,322,117,000	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to common stockholders	154,333,000			154,333,000	1,886,000	156,219,000
Comprehensive income	156,219,000
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(2,427,000)		(2,427,000)			(2,427,000)
Stock Issued During Period, Shares, New Issues		1,112,363
Stock Issued During Period, Value, New Issues	81,784,000	$ 12,000	81,772,000			81,784,000
Adjustments Related to Tax Withholding for Share-based Compensation			(1,835,000)
Equity Issuance Costs	(1,835,000)					(1,835,000)
Shares issued on stock options exercised, shares		55,894
Share-based Compensation			2,490,000
Share-based compensation	2,490,000					2,490,000
Dividends declared, $1.43 per share	$ (168,635,000)			(168,635,000)		(168,635,000)
Balance, shares at Dec. 31, 2018	42,700,411	42,700,411
Balance, value at Dec. 31, 2018	$ 1,389,713,000	$ 427,000	$ 1,369,919,000	$ 18,068,000	$ 1,299,000	$ 1,389,713,000	$ 0
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 235,000