Benefit Plans - Changes in Restricted Stock Awards Outstanding (Detail) (Restricted Stock [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Outstanding at beginning of year (in shares)	1,709,312	1,492,060	316,488
Granted (in shares)	1,488,960	479,541	1,423,152
Vested (in shares)	(524,663)	(217,305)	(192,870)
Forfeited (in shares)	(98,993)	(44,984)	(54,710)
Outstanding at end of year (in shares)	2,574,616	1,709,312	1,492,060