Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended						9 Months Ended
	Oct. 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)				48,065				48,065
Balance		$ 723,164	$ 714,129	$ 730,157	$ 695,257	$ 688,853	$ 699,221	$ 730,157	$ 699,221
Net income (loss)		42,424	16,996	(7,640)	36,173	14,805	(762)	$ 51,780	50,216
Issuance of common stock		1,866	1,675	3,179	853	737	636
Repurchase of common stock		(152)	(129)	(2,074)	(131)	(124)	(1,239)
Dividends paid on common stock		$ (9,507)	$ (9,507)	$ (9,493)	$ (9,012)	$ (9,014)	$ (9,003)
Dividends paid on common stock (in dollars per share)		$ 0.1975	$ 0.1975	$ 0.1975	$ 0.1875	$ 0.1875	$ 0.1875
Balance (in shares)		48,145						48,145
Balance		$ 757,795	$ 723,164	$ 714,129	$ 723,140	$ 695,257	$ 688,853	$ 757,795	$ 723,140
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance (in shares)		48,140	48,134	48,065	48,070	48,074	48,012	48,065	48,012
Balance		$ 481	$ 481	$ 481	$ 481	$ 481	$ 480	$ 481	$ 480
Issuance of common stock (in shares)		9	8	109	1		95
Issuance of common stock							$ 1
Repurchase of common stock (in shares)		(4)	(2)	(40)	(3)	(4)	(33)
Balance (in shares)		48,145	48,140	48,134	48,068	48,070	48,074	48,145	48,068
Balance		$ 481	$ 481	$ 481	$ 481	$ 481	$ 481	$ 481	$ 481
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		340,274	338,728	337,623	336,238	335,625	336,229	337,623	336,229
Issuance of common stock		1,866	1,675	3,179	853	737	635
Repurchase of common stock		(152)	(129)	(2,074)	(131)	(124)	(1,239)
Balance		341,988	340,274	338,728	336,960	336,238	335,625	341,988	336,960
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance		382,409	374,920	392,053	358,538	352,747	362,512	392,053	362,512
Net income (loss)		42,424	16,996	(7,640)	36,173	14,805	(762)
Dividends paid on common stock		(9,507)	(9,507)	(9,493)	(9,012)	(9,014)	(9,003)
Balance		$ 415,326	$ 382,409	$ 374,920	$ 385,699	$ 358,538	$ 352,747	$ 415,326	$ 385,699
Subsequent Event
Class of Stock [Line Items]
Equity Issuance, Amount Authorized	$ 300,000
Equity Issuance, Term	3 years