Stockholders' Equity and Earnings Per Share (Earnings Per Share Calculation) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 17, 2014	Jan. 16, 2014
Basic:
Net income	$ 99,352	$ 150,380	$ 244,176	$ 314,404
Basic weighted-average number of shares outstanding (in shares)	141,486,000	145,546,000	143,150,000	145,402,000
Basic EPS (in dollars per share)	$ 0.70	$ 1.03	$ 1.71	$ 2.16
Diluted:
Net income	$ 99,352	$ 150,380	$ 244,176	$ 314,404
Basic weighted-average number of shares outstanding (in shares)	141,486,000	145,546,000	143,150,000	145,402,000
Diluted potential common shares (in shares)	341,000	506,000	410,000	614,000
Diluted weighted-average number of shares outstanding (in shares)	141,827,000	146,052,000	143,560,000	146,016,000
Diluted EPS (in dollars per share)	$ 0.70	$ 1.03	$ 1.70	$ 2.15
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