Cash, Cash Equivalents and Investments - Effective Maturity Dates of Available-For-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
1 Year	$ 101,870
1-2 Years	98,375
2-3 Years	111,649
3-4 Years	29,852
4-5 Years	7,743
5-7 Years	6,729
Fair value	356,218
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	45,025
1-2 Years	19,494
2-3 Years	61,676
3-4 Years	8,456
4-5 Years	2,213
Fair value	136,864
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	25,257
1-2 Years	31,111
2-3 Years	10,209
3-4 Years	7,530
4-5 Years	4,519
5-7 Years	5,217
Fair value	83,843
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	12,184
1-2 Years	17,388
2-3 Years	12,595
3-4 Years	4,530
5-7 Years	505
Fair value	47,202
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	10,043
1-2 Years	20,009
2-3 Years	15,980
Fair value	46,032
Covered Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	4,664
1-2 Years	961
3-4 Years	1,796
Fair value	7,421
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	2,998
1-2 Years	8,647
2-3 Years	7,935
3-4 Years	5,425
4-5 Years	1,011
5-7 Years	1,007
Fair value	27,023
Sovereign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
1 Year	1,699
1-2 Years	765
2-3 Years	3,254
3-4 Years	2,115
Fair value	$ 7,833