Consolidated Statement Of Equity - USD ($) $ in Thousands	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, 2014		37,485,902
Balance, value at Dec. 31, 2014	$ 1,049,933	$ 375	$ 1,033,896	$ (569)	$ 6,223	$ 1,039,925	$ 10,008
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to common stockholders	148,862			148,862	21,687	170,549	1,452
Comprehensive income	172,001
Distributions to noncontrolling interest	(2,292)						(2,292)
Stock Issued During Period, Shares, New Issues		830,506
Stock Issued During Period, Value, New Issues	49,389	$ 8	49,381			49,389
Payments of Stock Issuance Costs	(275)		275			275
Shares issued on stock options exercised, shares		80,319
Shares issued on stock options exercised, value	1	$ 1	0			1
Share-based Compensation			2,134
Share-based compensation	2,134					2,134
Dividends declared, $1.43 per share	(128,431)			(128,431)		(128,431)
Balance, shares at Dec. 31, 2015		38,396,727
Balance, value at Dec. 31, 2015	1,142,460	$ 384	1,085,136	19,862	27,910	1,133,292	9,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to common stockholders	151,540			151,540	(22,179)	129,361	1,176
Comprehensive income	130,537
Distributions to noncontrolling interest	(1,565)						(1,565)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	(25,100)		(16,321)			(16,321)	(8,779)
Stock Issued During Period, Shares, New Issues		1,395,642
Stock Issued During Period, Value, New Issues	104,190	$ 14	104,176			104,190
Adjustments Related to Tax Withholding for Share-based Compensation	(1,133)		(1,133)			(1,133)
Shares issued on stock options exercised, shares		55,491
Shares issued on stock options exercised, value	(2)	$ 0	(2)			(2)
Share-based Compensation			1,732
Share-based compensation	1,732					1,732
Dividends declared, $1.43 per share	$ (141,529)			(141,529)		(141,529)
Balance, shares at Dec. 31, 2016	39,847,860	39,847,860
Balance, value at Dec. 31, 2016	$ 1,209,590	$ 398	1,173,588	29,873	5,731	1,209,590	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to common stockholders	159,365			159,365	(6,553)	152,812
Comprehensive income	152,812
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(7,930)		(7,930)			(7,930)
Stock Issued During Period, Shares, New Issues		1,661,161
Stock Issued During Period, Value, New Issues	122,237	$ 17	122,220			122,237
Adjustments Related to Tax Withholding for Share-based Compensation			(571)
Equity Issuance Costs	(571)					(571)
Shares issued on stock options exercised, shares		23,133
Shares issued on stock options exercised, value	0	$ 0				0
Share-based Compensation			2,612
Share-based compensation	2,612					2,612
Dividends declared, $1.43 per share	$ (156,633)			(156,633)		(156,633)
Balance, shares at Dec. 31, 2017	41,532,154	41,532,154
Balance, value at Dec. 31, 2017	$ 1,322,117	$ 415	$ 1,289,919	$ 32,605	$ (822)	$ 1,322,117	$ 0