Stockholders' Equity (Changes in Common Stock Shares Outstanding) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common stock shares outstanding:
Total stockholders’ equity	$ 1,832,174	$ 1,721,828
Total stockholders’ equity	1,900,777	1,832,174	$ 1,721,828
Common Stock
Common stock shares outstanding:
Total stockholders’ equity	3,636	3,636
Shares exercised under stock option plan	0	0	0
Total stockholders’ equity	$ 3,636	$ 3,636	$ 3,636