Accumulated Other Comprehensive (Loss) Income - Summary of Changes in Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance at beginning period			$ 686,799
Total other comprehensive income (loss), net of tax	$ (247)	$ 1,979	(3,698)	$ 1,980
Balance at period end	566,754		566,754
Unrealized Gain and (Loss) on Available-for-Sale Securities
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance at beginning period			2,507
Other comprehensive income before reclassifications			2,443
Amounts reclassified from accumulated other comprehensive loss			(6,141)
Total other comprehensive income (loss), net of tax			(3,698)
Balance at period end	$ (1,191)		$ (1,191)