Accumulated Other Comprehensive Loss - Summary of Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unrealized gains on debt securities:
Unrealized gains on available-for-sale investments before-tax amount	$ 5,650	$ (1,455)	$ (2,032)
Unrealized gains on available-for-sale investments tax benefit or (expense)	(2,222)	947
Unrealized gains on available-for-sale investments net-of-tax amount	3,428	(508)
Less: reclassification adjustment for other-than-temporary impairment losses included in earnings before-tax amount	0	1,295	0
Less: reclassification adjustment for other-than-temporary impairment losses included in earnings tax benefit or (expense)		(499)
Less: reclassification adjustment for other-than-temporary impairment losses included in earnings net-of-tax amount		796
Less: reclassification adjustment for gains included in earnings before-tax amount	(5,311)	833	(93)
Less: reclassification adjustment for gains included in earnings tax benefit or (expense)	2,522	(321)
Less: reclassification adjustment for gains included in earnings net-of-tax amount	(2,789)	512
Total before income taxes	339	673	(2,125)
Net unrealized gains tax benefit or (expense)	300	127
Net unrealized gains net-of-tax amount	639	800
Defined benefit pension plan:
Settlement included in net periodic cost before-tax amount		7,107
Settlement included in net periodic cost tax benefit or (expense)		0
Settlement included in net periodic cost net-of-tax amount	0	7,107	743
Less: amortization of loss included in net periodic pension cost before-tax amount	0	465	326
Less: amortization of loss included in net periodic pension cost tax benefit or (expense)		0
Less: amortization of loss included in net periodic pension cost net-of-tax amount		465
Net periodic pension cost arising during period before-tax amount		7,572
Net periodic pension cost arising during period tax benefit or (expense)		0
Net periodic pension cost arising during period net-of-tax amount		7,572
Net loss arising during period before-tax amount		(2,180)
Net loss arising during period tax benefit or (expense)		0
Net loss arising during period net-of-tax amount	0	2,180	(2,191)
Total before income taxes	0	5,392	3,260
Defined benefit pension plan, net tax benefit or (expense)	0	0	0
Total	0	5,392	3,260
Other comprehensive income before-tax amount	339	6,065
Other comprehensive income tax benefit or (expense)	300	127
Total other comprehensive income, net of tax	$ 639	$ 6,192	$ 1,135