Net Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Comprehensive Income [Line Items]
Balance at January 1, 2013			$ 20,258	$ 20,006
Other comprehensive income before reclassification, net of tax			(14,990)	2,370
Reclassifications from accumulated other comprehensive income, net of tax			71	276
Current period change in other comprehensive income, net of tax	(625)	1,737	(14,919)	2,646
Balance at September 30, 2013	5,339	22,652	5,339	22,652
Balance at January 1, 2013			(8,946)	(6,758)
Other comprehensive income before reclassification, net of tax			0	0
Reclassifications from accumulated other comprehensive income, net of tax			715	539
Current period change in other comprehensive income, net of tax	158	119	715	539
Balance at September 30, 2013	(8,231)	(6,219)	(8,231)	(6,219)
Balance at January 1, 2013			11,312	13,248
Other comprehensive income before reclassification, net of tax			(14,990)	2,370
Reclassifications from accumulated other comprehensive income, net of tax			786	815
Current period change in other comprehensive income, net of tax			(14,204)	3,185
Balance at September 30, 2013	$ (2,892)	$ 16,433	$ (2,892)	$ 16,433