Stockholders’ Equity and Earnings Per Share (Earnings Per Share Calculations) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 17, 2014	Jan. 16, 2014
Basic:
Net income									$ 674,035	$ 703,701	$ 505,624
Basic weighted average common shares outstanding (in shares)	145,624,000	145,559,000	145,546,000	145,256,000	144,960,000	144,921,000	144,899,000	144,664,000	145,497,000	144,862,000	144,444,000
Basic EPS (in dollars per share)	$ 1.29	$ 1.18	$ 1.03	$ 1.13	$ 1.19	$ 1.18	$ 1.19	$ 1.29	$ 4.63	$ 4.86	$ 3.50
Diluted:
Net income									$ 674,035	$ 703,701	$ 505,624
Basic weighted average common shares outstanding (in shares)	145,624,000	145,559,000	145,546,000	145,256,000	144,960,000	144,921,000	144,899,000	144,664,000	145,497,000	144,862,000	144,444,000
Diluted potential common shares (in shares)									682,000	1,307,000	1,469,000
Diluted weighted average common shares outstanding (in shares)	146,318,000	146,120,000	146,052,000	145,921,000	146,133,000	146,173,000	146,091,000	145,939,000	146,179,000	146,169,000	145,913,000
Diluted EPS (in dollars per share)	$ 1.29	$ 1.17	$ 1.03	$ 1.12	$ 1.18	$ 1.17	$ 1.18	$ 1.28	$ 4.61	$ 4.81	$ 3.47
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