Investments in debt and equity securities available-for-sale - Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	$ 20,456	$ 14,764
Gross unrealized losses	1,911	6,254
Municipal
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,097	258
Gross unrealized losses	120	813
Corporate
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	11,958	9,955
Gross unrealized losses	1,051	3,228
Foreign
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,601	363
Gross unrealized losses	336	2,142
U.S. Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	590	924
Gross unrealized losses	40	60
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	5,210	3,264
Gross unrealized losses	$ 364	$ 11