Note Net income per common share (Computation of net income (loss) per common share ("EPS"), basic and diluted) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Net Income	$ 279,783	$ 96,226	$ 371,107	$ 189,171
Preferred stock dividends	(931)	(931)	(1,862)	(1,862)
Net income (loss) applicable to common stock	$ 278,852	$ 95,295	$ 369,245	$ 187,309
Average common shares outstanding	101,892,402	101,601,552	101,794,914	102,263,593
Average potential dilutive common shares	139,553	107,151	137,563	123,653
Average common shares outstanding - assuming dilution	102,031,955	101,708,703	101,932,477	102,387,246
Net Income per Common Share - Basic	$ 2.74	$ 0.94	$ 3.63	$ 1.83
Net Income per Common Share - Diluted	$ 2.73	$ 0.94	$ 3.62	$ 1.83