STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Shares issued, beginning balance at Dec. 31, 2018		52,598,005
Equity, beginning balance at Dec. 31, 2018	$ 2,042,656	$ 526	$ 1,727,492	$ 320,869	$ (2,145)	$ (4,086)
Net income	93,660	0	0	93,660
Other comprehensive income	160	$ 0	0			160
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle				1,218		(1,218)
Common stock issued, shares		88,629
Common stock issued, value	(5,353)	$ 1	(7,499)		2,145
Common stock dividends - $0.54 and $0.50 per share per quarter as of 2020 and 2019, respectively	(26,343)	$ 0	227	(26,570)
Shares issued, ending balance at Mar. 31, 2019		52,686,634
Equity, ending balance at Mar. 31, 2019	2,104,780	$ 527	1,720,220	389,177	0	(5,144)
Shares issued, beginning balance at Dec. 31, 2018		52,598,005
Equity, beginning balance at Dec. 31, 2018	2,042,656	$ 526	1,727,492	320,869	(2,145)	(4,086)
Net income	135,587
Other comprehensive income	480
Shares issued, ending balance at Sep. 30, 2019		52,736,623
Equity, ending balance at Sep. 30, 2019	2,101,881	$ 527	1,728,237	377,941	0	(4,824)
Shares issued, beginning balance at Mar. 31, 2019		52,686,634
Equity, beginning balance at Mar. 31, 2019	2,104,780	$ 527	1,720,220	389,177	0	(5,144)
Net income	24,470	0		24,470	0	0
Other comprehensive income	160	$ 0		0		160
Common stock issued, shares		47,588
Common stock issued, value	5,397	$ 0	5,397	0	0	0
Common stock dividends - $0.54 and $0.50 per share per quarter as of 2020 and 2019, respectively	(26,344)	$ 0	226	(26,570)	0	0
Shares issued, ending balance at Jun. 30, 2019		52,734,222
Equity, ending balance at Jun. 30, 2019	2,108,463	$ 527	1,725,843	387,077	0	(4,984)
Net income	17,457	0		17,457	0	0
Other comprehensive income	160	$ 0		0		160
Common stock issued, shares		2,401
Common stock issued, value	2,169	$ 0	2,169	0	0	0
Common stock dividends - $0.54 and $0.50 per share per quarter as of 2020 and 2019, respectively	(26,368)	$ 0	225	(26,593)	0	0
Shares issued, ending balance at Sep. 30, 2019		52,736,623
Equity, ending balance at Sep. 30, 2019	$ 2,101,881	$ 527	1,728,237	377,941	0	(4,824)
Shares issued, beginning balance at Dec. 31, 2019	52,771,749	52,771,749
Equity, beginning balance at Dec. 31, 2019	$ 2,129,390	$ 528	1,733,092	402,509	0	(6,739)
Net income	91,677	0	0	91,677	0	0
Other comprehensive income	224	$ 0	0	0	0	224
Common stock issued, shares		89,059
Common stock issued, value	(3,736)	$ 1	(3,737)	0	0	0
Common stock dividends - $0.54 and $0.50 per share per quarter as of 2020 and 2019, respectively	(28,543)	$ 0	232	(28,775)	0	0
Shares issued, ending balance at Mar. 31, 2020		52,860,808
Equity, ending balance at Mar. 31, 2020	$ 2,189,012	$ 529	1,729,587	465,411	0	(6,515)
Document Period End Date	Sep. 30, 2020
Shares issued, beginning balance at Dec. 31, 2019	52,771,749	52,771,749
Equity, beginning balance at Dec. 31, 2019	$ 2,129,390	$ 528	1,733,092	402,509	0	(6,739)
Net income	138,081
Other comprehensive income	$ 670
Shares issued, ending balance at Sep. 30, 2020	53,096,893	53,096,893
Equity, ending balance at Sep. 30, 2020	$ 2,200,017	$ 531	1,751,350	454,205	0	(6,069)
Shares issued, beginning balance at Mar. 31, 2020		52,860,808
Equity, beginning balance at Mar. 31, 2020	2,189,012	$ 529	1,729,587	465,411	0	(6,515)
Net income	25,325	0	0	25,325	0	0
Other comprehensive income	223	$ 0	0	0	0	223
Common stock issued, shares		59,722
Common stock issued, value	5,974	$ 0	5,974	0	0	0
Common stock dividends - $0.54 and $0.50 per share per quarter as of 2020 and 2019, respectively	(28,547)	$ 0	227	(28,774)	0	0
Shares issued, ending balance at Jun. 30, 2020		52,920,530
Equity, ending balance at Jun. 30, 2020	2,191,987	$ 529	1,735,788	461,962	0	(6,292)
Net income	21,079	0	0	21,079	0	0
Other comprehensive income	223	$ 0	0	0	0	223
Common stock issued, shares		176,363
Common stock issued, value	15,336	$ 2	15,334	0	0	0
Common stock dividends - $0.54 and $0.50 per share per quarter as of 2020 and 2019, respectively	$ (28,608)	$ 0	228	(28,836)	0	0
Shares issued, ending balance at Sep. 30, 2020	53,096,893	53,096,893
Equity, ending balance at Sep. 30, 2020	$ 2,200,017	$ 531	$ 1,751,350	$ 454,205	$ 0	$ (6,069)