Stockholders' Equity and Earnings Per Share (Earnings Per Share Calculation) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 17, 2014	Jan. 16, 2014
Basic:
Net income	$ 144,824	$ 164,024
Basic weighted-average number of shares outstanding (in shares)	144,814,000	145,256,000
Basic EPS (in dollars per share)	$ 1.00	$ 1.13
Diluted:
Net income	$ 144,824	$ 164,024
Basic weighted-average number of shares outstanding (in shares)	144,814,000	145,256,000
Diluted potential common shares (in shares)	471,000	665,000
Diluted weighted-average number of shares outstanding (in shares)	145,285,000	145,921,000
Diluted EPS (in dollars per share)	$ 1.00	$ 1.12
Common Stock
Diluted:
Shares of common stock into which the warrant may be converted (in shares)			230,282
MetroCorp | MetroCorp
Diluted:
Shares of common stock into which the warrant may be converted (in shares)				771,429