Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Earnings in Excess of Distributions	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Beginning Balance at Dec. 31, 2014	$ 1,045,993	$ 1,113	$ 865,685	$ 206,342	$ (27,461)	$ 314
Beginning Balance, Shares at Dec. 31, 2014		111,287
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised	2,775	$ 2	2,773
Proceeds from stock options exercised, Shares		185
Tax benefit related to equity compensation	1,409		1,409
Stock based compensation expense	11,709		11,709
Shares withheld for net settlements of share-based awards, shares		(108)
Shares withheld for net settlements of share-based awards	(2,786)		(2,786)
Restricted stock granted	0	$ 6	(6)
Restricted stock granted, Shares		635
Restricted stock cancelled	0
Restricted stock cancelled, Shares		(53)
Dividends - Paid	(186,984)			(186,984)
Re-issuance of treasury shares (ESPP), Shares		20
Re-issuance of treasury shares (ESPP)	441		441	0
Net income (loss)	139,315			139,438		(123)
Other comprehensive income (loss), net of tax	(5,035)				(4,943)	(92)
Ending Balance at Dec. 31, 2015	1,006,837	$ 1,121	879,225	158,796	(32,404)	99
Ending Balance, Shares at Dec. 31, 2015		111,966
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised	3,347	$ 2	3,345
Proceeds from stock options exercised, Shares		234
Tax benefit related to equity compensation	(1,626)		(1,626)
Stock based compensation expense	12,773		12,773
Shares withheld for net settlements of share-based awards, shares		(113)
Shares withheld for net settlements of share-based awards	(2,337)		(2,335)
Restricted stock granted	0	$ 5	(5)
Restricted stock granted, Shares		523
Restricted stock cancelled	0	$ (1)	1
Restricted stock cancelled, Shares		(84)
Dividends - Paid	(194,748)			(194,748)
Re-issuance of treasury shares (ESPP), Shares		22
Re-issuance of treasury shares (ESPP)	436		436	0
Net income (loss)	148,498			148,715		(217)
Other comprehensive income (loss), net of tax	1,598				1,579	19
Ending Balance at Dec. 31, 2016	974,957	$ 1,125	891,993	112,763	(30,825)	(99)
Ending Balance, Shares at Dec. 31, 2016		112,548
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock options exercised	$ 6,962	$ 4	6,958
Proceeds from stock options exercised, Shares	360	358
Stock based compensation expense	$ 19,844		19,844
Shares withheld for net settlements of share-based awards, shares		(136)
Shares withheld for net settlements of share-based awards	(4,142)	$ (1)	(4,141)
Restricted stock granted	0	$ 9	(9)
Restricted stock granted, Shares		933
Restricted stock cancelled	0	$ (1)	1
Restricted stock cancelled, Shares		(65)
Dividends - Paid	(227,463)			(227,463)
Issuance of common stock under prospectus supplement	275,867	$ 104	275,763
Issuance of common stock under prospectus supplement, shares		10,350
Shares issued for ESPP		20
Issuance of common stock (ESPP)	497		497
Net income (loss)	146,024			146,241		(217)
Other comprehensive income (loss), net of tax	6,373				6,379	(6)
Ending Balance at Dec. 31, 2017	$ 1,198,919	$ 1,240	$ 1,190,906	$ 31,541	$ (24,446)	$ (322)
Ending Balance, Shares at Dec. 31, 2017		124,008