Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net change in Unrealized gains (losses), tax expense (benefit)	$ 5,932	$ (11,840)	$ 11,536	$ (14,738)
Reclassification adjustment for losses (gains), tax (benefit) expense	139	344	358	969
Change in unfunded pension liability related to unrealized loss, prior service cost and transition obligation, tax expense	$ 36	$ 0	$ 36	$ 0