Fair value measurements (Detail) $ in Thousands | Mar. 31, 2016USD ($)input | Dec. 31, 2015USD ($) |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | $ 626,363 | $ 579,849 |
Level 2 | Corporate | Minimum | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Number of inputs used in fair value measurement | input | 3 | |
Level 2 | Corporate | Maximum | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Number of inputs used in fair value measurement | input | 10 | |
Fair Value, Measurements, Recurring | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | $ 626,363 | 579,849 |
Fair Value, Measurements, Recurring | Municipal | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 72,397 | 72,008 |
Fair Value, Measurements, Recurring | Corporate | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 346,654 | 309,461 |
Fair Value, Measurements, Recurring | Foreign | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 161,484 | 153,221 |
Fair Value, Measurements, Recurring | U.S. Treasury Bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 13,894 | 13,906 |
Fair Value, Measurements, Recurring | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 31,934 | 31,253 |
Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 31,934 | 31,253 |
Fair Value, Measurements, Recurring | Level 1 | Municipal | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Corporate | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Foreign | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury Bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 31,934 | 31,253 |
Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 594,429 | 548,596 |
Fair Value, Measurements, Recurring | Level 2 | Municipal | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 72,397 | 72,008 |
Fair Value, Measurements, Recurring | Level 2 | Corporate | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 346,654 | 309,461 |
Fair Value, Measurements, Recurring | Level 2 | Foreign | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 161,484 | 153,221 |
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury Bonds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | 13,894 | 13,906 |
Fair Value, Measurements, Recurring | Level 2 | Equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale securities, fair value measurements | $ 0 | $ 0 |