Fair Value Measurements Fair Value Hierarchy (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | $ 191,030 | $ 153,509 |
Certificates of Deposit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 20,000 | |
Corporate bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 1,000 |
US treasury notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 10,875 |
Agency bond securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 14,904 | |
Municipal bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 583 | 739 |
Asset-backed securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 38,675 | 20,861 |
Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 191,030 | 153,509 |
Contingent consideration, fair value | 14,664 | 17,358 |
Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Contingent consideration, fair value | 0 | 0 |
Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 191,030 | 153,509 |
Contingent consideration, fair value | 0 | 0 |
Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Contingent consideration, fair value | 14,664 | 17,358 |
Recurring [Member] | Certificates of Deposit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 20,000 | |
Recurring [Member] | Certificates of Deposit [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | |
Recurring [Member] | Certificates of Deposit [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 20,000 | |
Recurring [Member] | Certificates of Deposit [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | |
Recurring [Member] | Corporate bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 1,000 |
Recurring [Member] | Corporate bonds [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 0 |
Recurring [Member] | Corporate bonds [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 1,000 |
Recurring [Member] | Corporate bonds [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 0 |
Recurring [Member] | US treasury notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 10,875 |
Recurring [Member] | US treasury notes [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 0 |
Recurring [Member] | US treasury notes [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 10,875 |
Recurring [Member] | US treasury notes [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | | 0 |
Recurring [Member] | Agency bond securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 14,904 | |
Recurring [Member] | Agency bond securities [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | |
Recurring [Member] | Agency bond securities [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 14,904 | |
Recurring [Member] | Agency bond securities [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | |
Recurring [Member] | Mortgage-backed securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 116,868 | 120,034 |
Recurring [Member] | Mortgage-backed securities [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Recurring [Member] | Mortgage-backed securities [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 116,868 | 120,034 |
Recurring [Member] | Mortgage-backed securities [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Recurring [Member] | Municipal bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 583 | 739 |
Recurring [Member] | Municipal bonds [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Recurring [Member] | Municipal bonds [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 583 | 739 |
Recurring [Member] | Municipal bonds [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Recurring [Member] | Asset-backed securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 38,675 | 20,861 |
Recurring [Member] | Asset-backed securities [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 0 | 0 |
Recurring [Member] | Asset-backed securities [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | 38,675 | 20,861 |
Recurring [Member] | Asset-backed securities [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, fair value | $ 0 | $ 0 |