Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance at December 31, 2016	$ 686,799
Total other comprehensive income (loss), net of tax	712	$ (54)
Ending Balance at March 31, 2017	657,562
Unrealized Gain and (Loss) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance at December 31, 2016	2,507
Other comprehensive income before reclassifications	2,405
Amounts reclassified from accumulated other comprehensive income	(1,693)
Total other comprehensive income (loss), net of tax	712
Ending Balance at March 31, 2017	$ 3,219