Shareholders' Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			$ 1,023,976
Proceeds from exercise of stock options, value			5,531
Proceeds from exercise of stock options, shares			293
Tax benefit related to equity compensation			1,351
Stock-based compensation expense			4,533
Restricted stock granted, value			0
Dividends paid			(82,656)
Re-issuance of treasury shares (ESPP), value			184
Net income	38,898	34,219	66,894	57,657
Other comprehensive loss	641	(5,260)	1,683	(6,440)
Ending Balance	1,020,080		1,020,080
Common shares
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			866
Beginning Balance, shares			72,082
Proceeds from exercise of stock options, value			3
Proceeds from exercise of stock options, shares			293
Restricted stock granted, value			3
Restricted stock granted, shares			308
Treasury Stock, Shares, Acquired			(43)
Re-issuance of treasury shares (ESPP), shares			6
Stock Repurchased and Retired During Period, Shares			0
Stock Repurchased and Retired During Period, Value			(146)
Ending Balance	726		726
Ending Balance, shares	72,633		72,633
Additional Paid-In Capital
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			848,018
Proceeds from exercise of stock options, value			5,528
Tax benefit related to equity compensation			1,351
Stock-based compensation expense			4,533
Restricted stock granted, value			(3)
Re-issuance of treasury shares (ESPP), value			161
Stock Repurchased and Retired During Period, Value			(54,826)
Ending Balance	804,762		804,762
Earnings in Excess of Distributions
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			232,646
Dividends paid			(82,656)
Re-issuance of treasury shares (ESPP), value
Stock Repurchased and Retired During Period, Value
Net income			66,888
Other comprehensive loss			0
Ending Balance	216,878		216,878
Accumulated Other Comprehensive Income (Loss)
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			(4,429)
Other comprehensive loss			1,687
Ending Balance	(2,742)		(2,742)
Treasury shares
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			(53,579)
Beginning Balance, shares			14,581
Treasury Stock, Shares, Acquired			43
Treasury Stock, Value, Acquired, Cost Method			1,416
Re-issuance of treasury shares (ESPP), value			23
Re-issuance of treasury shares (ESPP), shares			(6)
Stock Repurchased and Retired During Period, Shares			(14,618)
Stock Repurchased and Retired During Period, Value			54,972
Ending Balance	0		0
Ending Balance, shares	0		0
Noncontrolling Interests
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			454
Net income			6
Other comprehensive loss			(4)
Ending Balance	456		456
Stockholders' Equity, Total
Changes in shareholders' equity that are attributable to the Company's shareholders and to non controlling interests
Beginning Balance			1,023,976
Treasury Stock, Value, Acquired, Cost Method			1,416
Stock Repurchased and Retired During Period, Value			$ 0