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, 2017		52,598,005
Equity, beginning balance at Dec. 31, 2017	$ 1,960,209	$ 526	$ 1,737,551	$ 246,121	$ (18,496)	$ (5,493)
Net income	90,835	0		90,835	0	0
Other comprehensive income	(80)	$ 0		0		(80)
Common stock issued, shares		0
Common stock issued, value	(5,879)	$ 0	(16,074)	0	10,195	0
Common stock dividends - $0.50 and $0.46 per share per quarter as of 2019 and 2018, respectively	(24,137)	$ 0	224	(24,361)	0	0
Shares issued, ending balance at Mar. 31, 2018		52,598,005
Equity, ending balance at Mar. 31, 2018	2,020,948	$ 526	1,721,701	312,595	(8,301)	(5,573)
Shares issued, beginning balance at Dec. 31, 2017		52,598,005
Equity, beginning balance at Dec. 31, 2017	1,960,209	$ 526	1,737,551	246,121	(18,496)	(5,493)
Net income	127,530
Other comprehensive income	326
Shares issued, ending balance at Sep. 30, 2018		52,598,005
Equity, ending balance at Sep. 30, 2018	2,016,624	$ 526	1,725,361	300,547	(4,643)	(5,167)
Shares issued, beginning balance at Mar. 31, 2018		52,598,005
Equity, beginning balance at Mar. 31, 2018	2,020,948	$ 526	1,721,701	312,595	(8,301)	(5,573)
Net income	20,419	0		20,419	0	0
Other comprehensive income	203	$ 0		0		203
Common stock issued, shares		0
Common stock issued, value	4,909	$ 0	1,867	0	3,042	0
Common stock dividends - $0.50 and $0.46 per share per quarter as of 2019 and 2018, respectively	(24,135)	$ 0	227	(24,362)	0	0
Shares issued, ending balance at Jun. 30, 2018		52,598,005
Equity, ending balance at Jun. 30, 2018	2,022,344	$ 526	1,723,795	308,652	(5,259)	(5,370)
Net income	16,276	0	0	16,276	0	0
Other comprehensive income	203	$ 0	0	0		203
Common stock issued, shares		0
Common stock issued, value	1,961	$ 0	1,345	0	616	0
Common stock dividends - $0.50 and $0.46 per share per quarter as of 2019 and 2018, respectively	(24,160)	$ 0	221	(24,381)	0	0
Shares issued, ending balance at Sep. 30, 2018		52,598,005
Equity, ending balance at Sep. 30, 2018	$ 2,016,624	$ 526	1,725,361	300,547	(4,643)	(5,167)
Shares issued, beginning balance at Dec. 31, 2018	52,598,005	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	0	0
Other comprehensive income	160	0	0	0	0	160
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle	0	$ 0	0	1,218	0	(1,218)
Common stock issued, shares		88,629
Common stock issued, value	(5,353)	$ 1	(7,499)	0	2,145	0
Common stock dividends - $0.50 and $0.46 per share per quarter as of 2019 and 2018, respectively	(26,343)	$ 0	227	(26,570)	0	0
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	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	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	0	24,470	0	0
Other comprehensive income	160	$ 0	0	0	0	160
Common stock issued, shares		47,588
Common stock issued, value	5,397	$ 0	5,397	0	0	0
Common stock dividends - $0.50 and $0.46 per share per quarter as of 2019 and 2018, 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	0	17,457	0	0
Other comprehensive income	160	$ 0	0	0	0	160
Common stock issued, shares		2,401
Common stock issued, value	2,169	$ 0	2,169	0	0	0
Common stock dividends - $0.50 and $0.46 per share per quarter as of 2019 and 2018, respectively	$ (26,368)	$ 0	225	(26,593)	0	0
Shares issued, ending balance at Sep. 30, 2019	52,736,623	52,736,623
Equity, ending balance at Sep. 30, 2019	$ 2,101,881	$ 527	$ 1,728,237	$ 377,941	$ 0	$ (4,824)