Stockholders' Equity - Common Stock (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) shares	Mar. 31, 2019 USD ($) shares
Shares Issued
Dividend reinvestment plan issuances (in shares) | shares	175,129	4,148,667
Option exercises (in shares) | shares		2,505
Equity shelf program issuances (in shares) | shares	6,799,978	3,060,865
Preferred stock conversions (in shares) | shares		12,712,452
Stock incentive plans, net of forfeitures (in shares) | shares	158,818	140,940
Totals (in shares) | shares	7,133,925	20,065,429
Average Price
Dividend reinvestment plan issuances (in USD per share)	84.54	75.04
Option exercises (in USD per share)		53.89
Equity shelf plan issuances (in USD per share)	86.48	74.22
Gross Proceeds
Dividend reinvestment plan issuances	$ 14,805	$ 311,301
Option exercises		135
Equity shelf plan issuances	588,072	227,180
Totals	602,877	538,616
Net Proceeds
Dividend reinvestment plan issuances	14,805	307,821
Option exercises		135
Equity shelf plan issuances	576,196	225,587
Totals	$ 591,001	$ 533,543