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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Net Income	$ 140,648	$ 20,664	$ 511,755	$ 209,835
Preferred stock dividends	(930)	(930)	(2,792)	(2,792)
Net income (loss) applicable to common stock	$ 139,718	$ 19,734	$ 508,963	$ 207,043
Average common shares outstanding	101,067,300	101,652,352	101,549,711	102,057,607
Average potential dilutive common shares	181,854	111,520	182,219	127,937
Average common shares outstanding - assuming dilution	101,249,154	101,763,872	101,731,930	102,185,544
Net Income per Common Share - Basic	$ 1.38	$ 0.19	$ 5.01	$ 2.03
Net Income per Common Share - Diluted	$ 1.38	$ 0.19	$ 5	$ 2.03