Shareholders' Equity (Details) - USD ($) $ in Thousands			3 Months Ended		9 Months Ended
	Mar. 13, 2017	Mar. 07, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance					$ 974,957
Proceeds from exercise of stock options, value					$ 6,786
Proceeds from exercise of stock options (shares)					348,000
Stock-based compensation expense					$ 14,852
Restricted stock granted, value					0
Restricted stock canceled					0
Dividends paid					(169,152)
Issuance of common stock - prospectus supplement					275,867
Issuance of common stock - prospectus supplement (shares)	10,350,000	9,000,000
Shares withheld for net settlements of share-based awards					(4,122)
Issuance of common stock - ESPP					382
Net income			$ 38,453	$ 43,674	109,761	$ 99,156
Other comprehensive income			1,625	$ 483	4,761	$ (2,983)
Ending Balance			1,214,092		1,214,092
Common shares
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance					$ 1,125
Beginning Balance, shares					112,548,000
Proceeds from exercise of stock options, value					$ 3
Proceeds from exercise of stock options (shares)					348,000
Restricted stock granted, value					$ 9
Restricted stock granted (shares)					927,000
Restricted stock canceled (shares)					(60,000)
Issuance of common stock - prospectus supplement					$ 104
Issuance of common stock - prospectus supplement (shares)					10,350,000
Shares withheld for net settlements of share-based awards					$ (1)
Shares withheld for net settlements of share-based awards (shares)					(135,000)
Re-issuance of treasury shares - ESPP (shares)					13,000
Ending Balance			$ 1,240		$ 1,240
Ending Balance, shares			123,991,000		123,991,000
Additional Paid-In Capital
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance					$ 891,993
Proceeds from exercise of stock options, value					6,783
Stock-based compensation expense					14,852
Restricted stock granted, value					(9)
Issuance of common stock - prospectus supplement					275,763
Shares withheld for net settlements of share-based awards					(4,121)
Issuance of common stock - ESPP					382
Ending Balance			$ 1,185,643		1,185,643
Earnings in Excess of Distributions
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance					112,763
Dividends paid					(169,152)
Net income					109,884
Ending Balance			53,495		53,495
Accumulated Other Comprehensive Loss
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance					(30,825)
Other comprehensive income					4,757
Ending Balance			(26,068)		(26,068)
Noncontrolling Interests
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance					(99)
Net income					(123)
Other comprehensive income					4
Ending Balance			$ (218)		$ (218)