Equity: Stockholders Equity Recap (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Shares	23,756	53,959	44,253
Total Equity, beginning balance	$ 2,287,423	$ 1,820,206
Net income available for common stock	103,808	133,004
Net income attributable to noncontrolling interest	(3,554)	(3,630)
Net income	107,362	136,634
Other comprehensive income	457	1,260
Dividends on common stock	(30,332)	(25,444)
Share-based compensation	538	755
Stock Issued During Period, Value, New Issues	19,999
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(289)
Cumulative Effect of New Accounting Principle in Period of Adoption	3,390
Dividend reinvestment and stock purchase plan		219
Other stock transactions		2
Distribution to noncontrolling interest	(4,846)	(5,648)
Total Equity, ending balance	$ 2,383,702	$ 1,927,984
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding	60,378,020	53,648,817	60,048,567	53,579,986
Total Equity, beginning balance	$ 60,049	$ 53,580
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	48,956	64,770
Share-based compensation	$ 49	$ 65
Stock Issued During Period, Shares, New Issues	280,497
Stock Issued During Period, Value, New Issues	$ 280
Stock Issued During Period, Shares, Dividend Reinvestment Plan		4,061
Dividend reinvestment and stock purchase plan		$ 4
Total Equity, ending balance	$ 60,378	$ 53,649
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Shares	23,756	53,959	44,253	39,064
Total Equity, beginning balance	$ (2,510)	$ (2,306)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	(20,497)	14,895
Share-based compensation	$ 1,078	$ (743)
Total Equity, ending balance	(1,432)	(3,049)
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	1,450,569	1,150,285
Share-based compensation	(589)	1,433
Stock Issued During Period, Value, New Issues	19,719
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(289)
Dividend reinvestment and stock purchase plan		215
Total Equity, ending balance	1,469,410	1,151,933
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	700,396	548,617
Net income available for common stock	103,808	133,004
Dividends on common stock	(30,332)	(25,444)
Cumulative Effect of New Accounting Principle in Period of Adoption	3,390
Other stock transactions		(16)
Total Equity, ending balance	777,262	656,161
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	(26,916)	(41,202)
Other comprehensive income	457	1,260
Other stock transactions		18
Total Equity, ending balance	(26,459)	(39,924)
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total Equity, beginning balance	105,835	111,232
Net income attributable to noncontrolling interest	3,554	3,630
Distribution to noncontrolling interest	(4,846)	(5,648)
Total Equity, ending balance	$ 104,543	$ 109,214