Investments in debt and equity securities available-for-sale - Gross Unrealized Gains and Losses (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	$ 20,199	$ 23,848
Gross unrealized losses	5,657	1,125
Municipal
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,373	1,125
Gross unrealized losses	56	92
Corporate
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	10,523	12,559
Gross unrealized losses	1,236	446
Foreign
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	4,373	3,690
Gross unrealized losses	342	104
U.S. Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	257	492
Gross unrealized losses	0	27
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	3,673	5,982
Gross unrealized losses	$ 4,023	$ 456