Marketable Securities Amortized Cost and Fair Value of Marketable Securities Classified by Stated Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 82,574	$ 112,458
Fair Value	82,648	112,544
Due in 1 year or less
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,302	59,384
Fair Value	39,347	59,448
Due in 1 - 2 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,579	21,628
Fair Value	12,591	21,641
Due in 2 - 3 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,615	10,063
Fair Value	10,610	10,060
Due in 3 - 4 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,526	0
Fair Value	1,531	0
Due in 4 - 9 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,095	7,587
Fair Value	6,118	7,610
Due in 9 - 20 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,534	1,629
Fair Value	1,549	1,639
Due in 20 - 33 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,923	12,167
Fair Value	$ 10,902	$ 12,146