Retirement Plan, Based on Measurement Date (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in plan assets:
Fair value of assets at end of year	$ 222,990
Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	126,841	142,614
Interest cost	5,895	5,455	5,885
Actuarial loss (gain)	31,544	(13,393)
Annuity payments	(5,827)	(6,300)
Settlements	(1,392)	(1,535)
Benefit obligation at end of year	157,061	126,841	142,614
Change in plan assets:
Fair value of assets at beginning of year	219,330	187,623
Actual return on plan assets	10,879	39,542
Contributions	0	0
Annuity payments	(5,827)	(6,300)
Settlements	(1,392)	(1,535)
Fair value of assets at end of year	222,990	219,330	187,623
Funded status (included in "Other assets")	65,929	92,489
Changes recognized in other comprehensive income for the year ended December 31:
Amortization of prior service cost	0	0
Amortization of actuarial loss	(3,289)	(9,406)
Net actuarial loss (gain) arising during the year	40,100	(36,346)
Total recognized in other comprehensive loss for the year (pre-tax)	36,811	(45,752)
Accumulated other comprehensive loss (pre-tax) not yet recognized in net periodic benefit cost at December 31:
Prior service cost	0	0
Actuarial loss, net	83,938	47,127
Total accumulated other comprehensive loss (pre-tax)	$ 83,938	$ 47,127