Investments in debt and equity securities available-for-sale - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Gains	$ 31,933	$ 18,179
Losses	1,063	3,714
Municipal
Schedule of Available-for-sale Securities [Line Items]
Gains	2,745	1,720
Losses	49	12
Corporate
Schedule of Available-for-sale Securities [Line Items]
Gains	17,241	7,700
Losses	82	2,109
Foreign
Schedule of Available-for-sale Securities [Line Items]
Gains	6,395	3,789
Losses	41	482
U.S. Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Gains	90	128
Losses	0	25
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Gains	5,462	4,842
Losses	$ 891	$ 1,086