Stockholders’ Equity and Earnings Per Share (Earnings Per Share Calculations) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 16, 2019	Jan. 17, 2014
Basic:
Net income	$ 567,797	$ 674,035	$ 703,701
Basic weighted average common shares outstanding (in shares)	142,336,000	145,497,000	144,862,000
Basic EPS (in dollars per share)	$ 3.99	$ 4.63	$ 4.86
Diluted:
Net income	$ 567,797	$ 674,035	$ 703,701
Basic weighted average common shares outstanding (in shares)	142,336,000	145,497,000	144,862,000
Diluted potential common shares (in shares)	655,000	682,000	1,307,000
Diluted weighted average common shares outstanding (in shares)	142,991,000	146,179,000	146,169,000
Diluted EPS (in dollars per share)	$ 3.97	$ 4.61	$ 4.81
Common Stock
Class of Stock
Shares of common stock into which the warrant may be converted (in shares)				230,282
MetroCorp | MetroCorp
Class of Stock
Shares of common stock into which the warrant may be converted (in shares)					771,429