Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at December 31, 2016			$ 686,799
Total other comprehensive income (loss), net of tax	$ (4,163)	$ 55	(3,451)	$ 1
Balance at June 30, 2017	657,866		657,866
Unrealized Gain and (Loss) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at December 31, 2016			2,507
Other comprehensive income before reclassifications			2,861
Amounts reclassified from accumulated other comprehensive loss			(6,312)
Total other comprehensive income (loss), net of tax			(3,451)
Balance at June 30, 2017	$ (944)		$ (944)