Statements of Change in Common Stock Equity Statement - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net of Tax	Treasury Stock	Restricted Stock	Restricted Stock Additional Paid-in Capital	Performance Shares	Performance Shares Additional Paid-in Capital
Balances at beginning of period (in shares) at Dec. 31, 2017		65,828,688				25,244,350
Balances at beginning of period at Dec. 31, 2017	$ 1,142,165	$ 65,829	$ 326,117	$ 1,159,667	$ 11,058	$ (420,506)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation grants of common stock, value							$ (47)	$ (560)	$ 1,499	$ 360
Stock based compensation, grants of common stock, treasury stock reissued (in share)							(30,800)		(68,379)
Stock based compensation, grants of common stock, treasury stock reissued, value							$ 513		$ 1,139
Stock awards withheld for taxes (in shares)						20,389
Stock awards withheld for taxes, value	(1,064)		(725)			$ (339)
Forfeited restricted common stock (in shares)						2,391
Forfeited restricted common stock, value	(40)					$ (40)
Compensation paid in shares (in shares)						(1,008)
Compensation paid in shares, value	52		35			$ 17
Net income	(6,966)			(6,966)
Other Comprehensive Income (Loss)	(2,351)				(2,351)
Common stock, dividends declared, cash	(13,615)			(13,615)
Balances at end of period (in shares) at Mar. 31, 2018		65,828,688				25,166,943
Balances at end of period at Mar. 31, 2018	1,119,633	$ 65,829	325,227	1,180,114	(32,321)	$ (419,216)
Balances at beginning of period (in shares) at Dec. 31, 2017		65,828,688				25,244,350
Balances at beginning of period at Dec. 31, 2017	1,142,165	$ 65,829	326,117	1,159,667	11,058	$ (420,506)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	26,329
Common stock, dividends declared, cash	(28,300)
Balances at end of period (in shares) at Jun. 30, 2018		65,828,688				25,135,367
Balances at end of period at Jun. 30, 2018	1,138,202	$ 65,829	326,042	1,198,767	(33,746)	$ (418,690)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for financial instruments	0			41,028	(41,028)
Balances at beginning of period (in shares) at Mar. 31, 2018		65,828,688				25,166,943
Balances at beginning of period at Mar. 31, 2018	1,119,633	$ 65,829	325,227	1,180,114	(32,321)	$ (419,216)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation grants of common stock, value							$ 1,294	777
Stock based compensation, grants of common stock, treasury stock reissued (in share)							(31,009)
Stock based compensation, grants of common stock, treasury stock reissued, value							$ 517
Forfeited restricted common stock (in shares)						335
Forfeited restricted common stock, value	(5)					$ (5)
Compensation paid in shares (in shares)						(902)
Compensation paid in shares, value	52		38			$ 14
Net income	33,295			33,295
Other Comprehensive Income (Loss)	(1,425)				(1,425)
Common stock, dividends declared, cash	(14,642)			(14,642)
Balances at end of period (in shares) at Jun. 30, 2018		65,828,688				25,135,367
Balances at end of period at Jun. 30, 2018	1,138,202	$ 65,829	326,042	1,198,767	(33,746)	$ (418,690)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	90,201
Common stock, dividends declared, cash	$ (59,600)
Balances at end of period (in shares) at Jun. 30, 2019	64,281,761	64,428,688				23,665,296
Balances at end of period at Jun. 30, 2019	$ 1,169,005	$ 64,429	321,506	1,212,962	(35,693)	$ (394,199)
Balances at beginning of period (in shares) at Dec. 31, 2018	65,707,156	65,828,688				25,147,567
Balances at beginning of period at Dec. 31, 2018	$ 1,164,103	$ 65,829	328,480	1,227,471	(38,784)	$ (418,893)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation grants of common stock, value							$ (804)	(1,328)	$ 2,143	$ 1,478
Stock based compensation, grants of common stock, treasury stock reissued (in share)							(31,461)		(39,923)
Stock based compensation, grants of common stock, treasury stock reissued, value							$ 524		$ 665
Stock awards withheld for taxes (in shares)						12,425
Stock awards withheld for taxes, value	(637)		(430)			$ (207)
Forfeited restricted common stock (in shares)						2,566
Forfeited restricted common stock, value	(43)					$ (43)
Compensation paid in shares (in shares)						(669)
Compensation paid in shares, value	39		28			$ 11
Net income	6,089			6,089
Other Comprehensive Income (Loss)	1,657				1,657
Common stock, dividends declared, cash	(14,658)			(14,658)
Balances at end of period (in shares) at Mar. 31, 2019		65,828,688				25,090,505
Balances at end of period at Mar. 31, 2019	$ 1,157,889	$ 65,829	328,228	1,218,902	(37,127)	$ (417,943)
Balances at beginning of period (in shares) at Dec. 31, 2018	65,707,156	65,828,688				25,147,567
Balances at beginning of period at Dec. 31, 2018	$ 1,164,103	$ 65,829	328,480	1,227,471	(38,784)	$ (418,893)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,215
Common stock, dividends declared, cash	$ (30,400)
Balances at end of period (in shares) at Jun. 30, 2019	64,281,761	64,428,688				23,665,296
Balances at end of period at Jun. 30, 2019	$ 1,169,005	$ 64,429	321,506	1,212,962	(35,693)	$ (394,199)
Balances at beginning of period (in shares) at Mar. 31, 2019		65,828,688				25,090,505
Balances at beginning of period at Mar. 31, 2019	1,157,889	$ 65,829	328,228	1,218,902	(37,127)	$ (417,943)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation grants of common stock, value							$ (797)	$ (1,205)
Stock based compensation, grants of common stock, treasury stock reissued (in share)							(24,500)
Stock based compensation, grants of common stock, treasury stock reissued, value							$ 408
Compensation paid in shares (in shares)						(709)
Compensation paid in shares, value	47		35			$ 12
Net income	26,126			26,126
Retirement of treasury shares, (in shares)		(1,400,000)				(1,400,000)
Retirement of treasury shares, value	0	$ (1,400)	(5,552)	(16,372)		$ (23,324)
Other Comprehensive Income (Loss)	1,434				1,434
Common stock, dividends declared, cash	$ (15,694)			(15,694)
Balances at end of period (in shares) at Jun. 30, 2019	64,281,761	64,428,688				23,665,296
Balances at end of period at Jun. 30, 2019	$ 1,169,005	$ 64,429	$ 321,506	$ 1,212,962	$ (35,693)	$ (394,199)