Stockholders' Equity - Changes in accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan	$ 0	$ 2,519	$ 0	$ 2,519
Forward-starting Interest Rate Swaps
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance			(1,569)	0
Other comprehensive income (loss) before reclassifications			0	(1,684)
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan			0
Amounts reclassified from accumulated other comprehensive loss			84	31
Net accumulated other comprehensive income (loss)			84	(1,653)
Ending balance	(1,485)	(1,653)	(1,485)	(1,653)
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance			0	(2,519)
Other comprehensive income (loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan			0	2,519
Amounts reclassified from accumulated other comprehensive loss			0	0
Net accumulated other comprehensive income (loss)			0	2,519
Ending balance	$ 0	$ 0	$ 0	$ 0