Shareholders' Equity (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	$ 1,198,919
Proceeds from exercise of stock options, value	$ 261
Proceeds from exercise of stock options (shares)	15
Stock-based compensation expense	$ 5,827
Restricted stock canceled	0
Dividends paid	(58,319)
Shares withheld for net settlements of share-based awards	(4,357)
Issuance of common stock - ESPP	141
Purchase of Treasury Shares	(40,182)
Net income	34,920	$ 40,366
Other comprehensive income	1,362	$ 1,260
Ending Balance	1,138,572
Common shares
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	$ 1,240
Beginning Balance, shares	124,008
Proceeds from exercise of stock options, value	$ 1
Proceeds from exercise of stock options (shares)	15
Restricted stock canceled	$ 0
Restricted stock canceled (shares)	(9)
Shares withheld for net settlements of share-based awards	$ (2)
Shares withheld for net settlements of share-based awards (shares)	(169)
Re-issuance of treasury shares - ESPP (shares)	8
Purchase of Treasury Shares (shares)	(1,848)
Ending Balance	$ 1,239
Ending Balance, shares	122,005
Additional Paid-In Capital
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	$ 1,190,906
Proceeds from exercise of stock options, value	260
Stock-based compensation expense	5,827
Shares withheld for net settlements of share-based awards	(4,355)
Issuance of common stock - ESPP	141
Ending Balance	1,192,779
Earnings in Excess of Distributions
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	31,541
Dividends paid	(58,319)
Net income	34,987
Ending Balance	8,209
Accumulated Other Comprehensive Loss
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	(24,446)
Other comprehensive income	1,354
Ending Balance	(23,092)
Treasury shares
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	$ 0
Beginning Balance, shares	0
Purchase of Treasury Shares	$ (40,182)
Purchase of Treasury Shares (shares)	1,848
Ending Balance	$ (40,182)
Ending Balance, shares	1,848
Noncontrolling Interests
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance	$ (322)
Net income	(67)
Other comprehensive income	8
Ending Balance	$ (381)