Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 755,140	$ 779,906	$ 714,129	$ 730,157	$ 779,906	$ 730,157
Net Income (Loss) Available to Common Stockholders, Basic	5,281	(20,307)	16,996	(7,640)	$ (15,026)	$ 9,356
Issuance of common stock	32,063	7,229	1,675	3,179
Repurchase of common stock	(105)	(1,373)	(129)	(2,074)
Dividends paid on common stock	$ (10,356)	$ (10,315)	$ (9,507)	$ (9,493)
Dividends paid on common stock (in dollars per share)	$ 0.2125	$ 0.2125	$ 0.1975	$ 0.1975
Balance at end of period (in shares)	49,398		48,532		49,398	48,532
Balance at end of period	$ 782,023	$ 755,140	$ 723,164	$ 714,129	$ 782,023	$ 723,164
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)	48,714,000	48,532,000	48,134,000	48,065,000	48,532,000	48,065,000
Balance at beginning of period	$ 487	$ 485	$ 481	$ 481	$ 485	$ 481
Issuance of common stock (in shares)	686,000	210,000	8,000	109,000
Issuance of common stock	$ 7	$ 2		$ 0
Repurchase of common stock (in shares)	(2,000)	(28,000)	(2,000)	(40,000)
Balance at end of period (in shares)	49,398,000	48,714,000	48,140,000	48,134,000	49,398,000	48,140,000
Balance at end of period	$ 494	$ 487	$ 481	$ 481	$ 494	$ 481
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	368,129	362,275	338,728	337,623	362,275	337,623
Issuance of common stock	32,056	7,227	1,675	3,179
Repurchase of common stock	(105)	(1,373)	(129)	(2,074)
Balance at end of period	400,080	368,129	340,274	338,728	400,080	340,274
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	386,524	417,146	374,920	392,053	417,146	392,053
Net Income (Loss) Available to Common Stockholders, Basic	5,281	(20,307)	16,996	(7,640)
Dividends paid on common stock	(10,356)	(10,315)	(9,507)	(9,493)
Balance at end of period	$ 381,449	$ 386,524	$ 382,409	$ 374,920	$ 381,449	$ 382,409