Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)			48,532,000				48,532,000
Balance at beginning of period	$ 782,023	$ 755,140	$ 779,906	$ 723,164	$ 714,129	$ 730,157	$ 779,906	$ 730,157
Net income	96,360	5,281	(20,307)	42,424	16,996	(7,640)	$ 81,334	51,780
Issuance of common stock	22,414	32,063	7,229	1,866	1,675	3,179
Repurchase of common stock	(99)	(105)	(1,373)	(152)	(129)	(2,074)
Dividends paid on common stock	$ (10,506)	(10,356)	(10,315)	(9,507)	(9,507)	(9,493)
Balance at end of period (in shares)	49,840,000						49,840,000
Balance at end of period	$ 890,192	$ 782,023	$ 755,140	$ 757,795	$ 723,164	$ 714,129	$ 890,192	$ 757,795
Dividends paid on common stock (in dollars per share)	$ 0.2125	$ 0.2125	$ 0.2125	$ 0.1975	$ 0.1975	$ 0.1975
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)	49,398,000	48,714,000	48,532,000	48,140,000	48,134,000	48,065,000	48,532,000	48,065,000
Balance at beginning of period	$ 494	$ 487	$ 485	$ 481	$ 481	$ 481	$ 485	$ 481
Issuance of common stock (in shares)	444,000	686,000	210,000	9,000	8,000	109,000
Issuance of common stock	$ 4	$ 7	$ 2
Repurchase of common stock (in shares)	(2,000)	(2,000)	(28,000)	(4,000)	(2,000)	(40,000)
Balance at end of period (in shares)	49,840,000	49,398,000	48,714,000	48,145,000	48,140,000	48,134,000	49,840,000	48,145,000
Balance at end of period	$ 498	$ 494	$ 487	$ 481	$ 481	$ 481	$ 498	$ 481
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	400,080	368,129	362,275	340,274	338,728	337,623	362,275	337,623
Issuance of common stock	22,410	32,056	7,227	1,866	1,675	3,179
Repurchase of common stock	(99)	(105)	(1,373)	(152)	(129)	(2,074)
Balance at end of period	422,391	400,080	368,129	341,988	340,274	338,728	422,391	341,988
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	381,449	386,524	417,146	382,409	374,920	392,053	417,146	392,053
Net income	96,360	5,281	(20,307)	42,424	16,996	(7,640)
Dividends paid on common stock	(10,506)	(10,356)	(10,315)	(9,507)	(9,507)	(9,493)
Balance at end of period	$ 467,303	$ 381,449	$ 386,524	$ 415,326	$ 382,409	$ 374,920	$ 467,303	$ 415,326