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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share, Basic and Diluted [Abstract]
Net Income	$ 20,664	$ 46,810	$ 209,835	$ 220,796
Preferred stock dividends	(930)	(930)	(2,792)	(2,792)
Net income (loss) applicable to common stock	$ 19,734	$ 45,880	$ 207,043	$ 218,004
Average common shares outstanding	101,652,352	103,296,443	102,057,607	103,243,851
Average potential dilutive common shares	111,520	168,942	127,937	140,098
Average common shares outstanding - assuming dilution	101,763,872	103,465,385	102,185,544	103,383,949
Net Income per Common Share - Basic	$ 0.19	$ 0.44	$ 2.03	$ 2.11
Net Income per Common Share - Diluted	$ 0.19	$ 0.44	$ 2.03	$ 2.11